FACTOEY  LIGHTING 


McGraw-Hill  BookCompany 


Electrical  World         TTie  Engineering  and  Mining  Journal 
Engineering  Record  Engineering  News 

Railway  Age  G  azett<?  American  Machinist 

Signal  Elngin<?er  American  Engineei* 

Electric  Railway  Journal  Coal  Age 

Metallurgical  and  Chemical  Engineering  P  o  we  r 


FACTORY  LIGHTING 


BY 
CLARENCE  E.  CLEWELL 

MEMBER  ILLUMINATING  ENGINEERING  SOCIETY 


McGRAW-HILL  BOOK  COMPANY,  INC. 

239  WEST  39TH  STREET,  NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.  C. 

1913 


COPYRIGHT,  1913,  BY  THE 
McGRAW-HiLL  BOOK  COMPANY,  INC. 


THE. MAPLE . PRESS- YORK. PA 


PREFACE 

Good  lighting  is  an  aid  to  accurate  workmanship  and  manu- 
facturing output,  and  contributes  to  a  reduction  in  manufactur- 
ing costs.  It  has  thus  become  a  distinct  feature  in  factory 
equipment.  This  book  aims  to  tell  in  a  simple  way  how  to  obtain 
good  lighting.  As  set  rules,  however,  are  apt  to  be  misleading, 
the  experiences  in  actual  installations  are  .made  the  basis  for 
analysis  and  explanation  so  that  they  may  be  useful  in  similar 
problems  under  varying  conditions. 

The  scheme  in  the  text  is  somewhat  of  a  departure  from  pre- 
vailing methods  in  the  treatment  of  illumination  information. 
Actual  results  are  given  precedence  over  generalized  statements 
and  the  practical  application  of  the  text  will  require,  therefore, 
a  selection  from  one  or  another  of  the  cases  described,  to  be  used 
as  a  guide  in  any  particular  class  of  work.  As  the  office,  the 
drafting  room  and  the  power  house  are  connected  with  the  fac- 
tory, they  are  included  under  the  general  title  Factory  Lighting. 

The  electric  lamp,  rather  than  gas,  is  the  type  to  which  at- 
tention is  given  since  it  is  in  very  general  use  for  factory  lighting 
and  furthermore  supplied  the  experience  which  forms  the  basis 
of  the  following  pages.  The  effect  produced  by  electric  lamps 
and  by  gas  lamps  involves  the  same  general  principles  of  illumi- 
nation, so  that  in  a  broad  sense  the  conclusions  reached  are 
equally  applicable  to  either  source  of  light. 

The  author  has  been  engaged  in  the  design  and  supervision 
of  the  installation  of  lighting  systems  during  a  number  of  years, 
principally  in  the  works  of  the  Westinghouse  Electric  and  Manu- 
facturing Company,  which  embody  a  wide  variety  of  manufactur- 
ing operations.  From  time  to  time  articles  relating  to  these 
installations  have  appeared  in  the  American  Machinist,  Cana- 
dian Manufacturer,  Electric  Journal,  and  Power.  Papers  may 
also  be  found  in  the  transactions  of  the  American  Institute  of 
Electrical  Engineers,  American  Society  of  Mechanical  Engineers, 
National  Electric  Light  Association  and  the  Association  of  Iron 
and  Steel  Electrical  Engineers.  Some  of  the  material  in  the 
following  pages  has  been  selected  from  portions  of  these  articles 


271055 


vi  PREFACE 

and  papers,  but  where  discussions  are  more  complete  in  the 
original  article,  a  reference  is  made  to  it. 

Appreciation  for  helpful  advice  is  due  Professor  Chas.  F. 
Scott,  Sheffield  Scientific  School  of  Yale  University,  with  whom 
many  of  the  experiences  discussed  have  been  shared.  The 
analysis  of  artificial  lighting  costs  in  terms  of  wages  as  pub- 
lished by  him  in  the  Electric  Journal  in  May,  1910,  emphasizes 
a  new  viewpoint  in  the  consideration  of  industrial  lighting.  The 
evaluation  of  lighting  costs  to  an  equivalent  proportion  of  the 
wages  has  become  a  common  method  of  expressing  the  advan- 
tages of  good  light  in  factory  work. 

The  author  is  also  under  obligation  to  Mr.  H.  M.  Ryder, 
Westinghouse  Electric  and  Manufacturing  Company,  for  assis- 
tance in  the  preparation  of  diagrams  used  as  illustrations  in  this 
volume. 

CLARENCE  E.  CLEWELL. 

SHEFFIELD  SCIENTIFIC  SCHOOL 

OF  YALE  UNIVERSITY, 

NEW  HAVEN,  CONN., 

June,  1913. 


CONTENTS 

PAGE 
PREFACE ,    .    .    .- v 

CHAPTER  I 

GENERAL  ITEMS  AND  REQUIREMENTS •'.       1 

New  ideas  regarding  factory  lighting — Practical  features — Classi- 
fication— The  influence  of  candle-power  and  physical  dimensions 
of  modern  lamps — Effective  illumination — Quality  of  light  and 
illumination. 

CHAPTER  II 

ILLUMINATION  DESIGN 6 

Scope  of  illumination  design — Inspection  of  the  location — Reflec- 
tors and  globes — Type  of  lamp — Size  of  lamp — Spacing  of  lamps 
— Mounting  height  of  lamps — Switch  control — The  working 
drawing — Lighting  system  efficiency — Point  addition  of  intensity 
values — Problem  illustrating  steps  in  typical  design. 

CHAPTER  III 

LIGHTING  INSTALLATION  WORK  ...»....„....'....  28 
Installation  of  a  lighting  system — Theory  and  practice — Installing 
lamps  according  to  a  fixed  plan — Estimating  the  cost  of  the  work — 
Relation  of  ceiling  construction  to  wiring  expense — Following  up 
the  work — Underwriter's  rules — Supporting  the  lamps  securely — 
Control  circuits — Series  and  multiple  systems — Supply  circuits — 
Methods  of  installation  in  relation  to  maintenance — Economy  in 
using  wiring  material — Tungsten  lamps  under  shop  conditions — 
Installing  small  numbers  of  lamps  at  a  time — Locating  the  outlets 
on  the  ceiling — Concluding  items. 

CHAPTER  IV 

LIGHTING  MAINTENANCE  AND  MAINTENANCE  RECORDS    .......     46 

Deterioration  of  lighting  equipment — Importance  of  systematic 
maintenance — Cost  relations  between  maintenance  and  losses  from 
lack  of  maintenance — Items  connected  with  the  maintenance — 
Inspecting  lighting  systems — Cleaning  reflectors  and  globes — 
Maintenance  records — Items  included  in  the  lighting  system — 
Record  charts — Simplicity  essential — Storage — Results  of  adher- 
ence to  these  principles. 

CHAPTER  V 

OFFICE  LIGHTING.    .    .    ....    .    .    .  -.    .....,.>.    *    .    ...    .  -.     65 

General  items — General  requirements  based  on  the  foregoing  con- 

vii 


viii  CONTENTS 

siderations — A  typical  office  investigated — Simple  rules — Design 
factors — High  ceilings — Offices  of  odd  dimensions — Narrow  office, 
15  by  35  ft.— Small  office,  10  ft.  by  12  ft.  6  in.— Rectangular  office, 
15  by  20  ft. 

CHAPTER  VI 

DRAFTING  ROOM  LIGHTING 85 

Difficult  conditions — General  requirements — Eliminating  shadows 
A  practical  investigation — Combined  direct  and  indirect  light — 
Illumination  features — Various  fixture  combinations — Other 
conditions. 

CHAPTER  VII 

FACTORY  LIGHTING 98 

New  ideas  regarding  factory  conditions — Various  items  concerning 
the  work  and  surroundings— General  requirements— Method  of  light- 
ing by  over-head  lamps — The  field  of  various  types  of  lamps — 
Glass  and  metal  reflectors  compared — Side  lighting — The  lighting 
circuits — A  practical  case  in  a  location  with  moderate  ceiling  height 
— A  practical  case  in  a  location  where  the  lamps  must  be  mounted 
very  high — Other  items — Cost  factors. 

CHAPTER  VIII 

POWER  HOUSE  LIGHTING 115 

Relations  of  lighting  to  operation — General  requirements — Econ- 
omy afforded  by  good  lighting — The  modern  viewpoint — Various 
locations  involved — A  practical  case  where  medium-sized  lamps 
are  used — Arc  and  mercury  vapor  lamps — Simple  principles  im- 
portant— Definite  rules  are  apt  to  mislead — Maintenance — Gen- 
eral hints — Summary. 

CHAPTER  IX 

IRON  AND  STEEL  MILL  LIGHTING 125 

General  items — Electrical  considerations — The  various  buildings 
involved — General  requirements — Peculiar  importance  of  over-head 
lighting — Adaptation  of  the  various  types  of  lamps — Specific  loca- 
tions involved — Other  items — Economy  of  superior  lighting 
facilities. 

CHAPTER  X 

MACHINE  TOOL  LIGHTING 144 

Importance  of  adequate  light  on  the  machine  tool — Cases  provided 
for  by  over-head  lamps — Points  on  the  mounting  of  individual 
lamps — Cost  relations  of  artificial  light  and  machine  tool  operation 
—Physical  size  of  the  individual  lamp — Extension  lines — Shadow 
contrasts — Candle-power  of  individual  lamps — Concluding  items. 

INDEX .57 


FACTORY  LIGHTING 

CHAPTER  I 
GENERAL  ITEMS  AND  REQUIREMENTS 

1.  New  Ideas  Regarding  Factory  Lighting. — The  inadequate 
means  available  for  illumination  in  the  past  has  contributed  to 
the  slowness  of  an  appreciation  of  the  features  of  artificial 
light  which  influence  the  working  efficiency  of  the  eye.  Gas, 
carbon  incandescent,  and  arc  lamps,  practically  the  only  illumi- 
nants  available  ten  years  ago,  play  but  a  small  part  in  the  pres- 
ent approved  methods  of  factory  lighting. 

The  large  variety  of  comparatively  new  electric  lamps  in- 
cludes the  Nernst,  mercury  vapor,  metallized  filament,  tanta- 
lum, tungsten,  Moore  tube,  metallic  flame  or  magnetite  arc,  the 
flame  carbon  arc  and  the  quartz  lamp.  Possibilities  in  factory 
lighting  are  now  attainable  which,  before  the  introduction  of 
these  new  lamps,  were  either  unthought  of,  or  impossible.  Con- 
sideration of  the  eye  as  a  delicate  organ,  together  with  the  new 
ideas  of  the  items  which  affect  its  comfort  and  efficiency,  have 
resulted  in  establishing  certain  principles  in  illumination  work, 
and  have  directed  attention  naturally  and  in  a  growing  manner 
to  the  proper  use  and  application  of  these  new  lamps. 

Another  item  has  been  the  increased  attention  to  the  general 
betterment  of  shop  conditions.  Besides  many  other  things  con- 
nected with  the  factory  equipment,  one  of  the  major  studies 
has  been  that  of  artificial  illumination  for  the  attainment  of 
several  well  defined  objects,  as  follows: 

(1)  Increased  production  for  the  same  labor  cost. 

(2)  Greater  accuracy  in  workmanship. 

(3)  Reduced  number  of  accidents. 

(4)  Less  eye  strain. 

(5)  More  cheerful  surroundings. 

(6)  Greater  comfort  for  the  workmen. 

(7)  More  order  and  neatness  in  the  shop. 

1 


FACTORY  LIGHTING 

(8)  Supervision  of  the  men  made  easier  on  dark  days  and 
at  night. 

The  term  light  in  the  past  has  been  used  to  designate  the  effect 
from  the  lamp  as  well  as  the  effect  on  the  work.  This  term  is 
now  used  by  common  acceptance  in  relation  to  the  lamp  alone, 
while  the  effect  in  rendering  objects  visible  is  called  the  illumi- 
nation. This  latter  term  will  be  used,  therefore,  in  reference 
to  the  result  produced  by  the  lamp  or  lamps  of  a  system.  The 
term  system  is  employed  because  in  the  typical  shop,  office  or 
drafting  room  the  floor  space  is  often  used  entirely  for  working 
operations.  Artificial  light  in  such  cases  is  sometimes  provided 
over  the  entire  area  of  floor  space  by  lamps  mounted  near  the 
ceiling,  so  that  a  given  object  receives  light  from  several  lamps, 
hence  the  term  system. 

2.  Practical  Features. — The  following  specific   requirements 
should  be  secured  in  factory  lighting  systems: 

(1)  Sufficient  illumination  should  be  provided  for  each  person. 

(2)  Uniform  illumination  should  in  most  cases  be  secured 
so  that  it  may  be  satisfactory  without  regard  to  the  location 
of    the    work;    that    is,    the    entire    working    surface    should 
be  illuminated. 

(3)  Hand  lamps,   as  distinguished  from  those  which  afford 
general  illumination,  should  be  eliminated  where  it  is  possible 
to  make  the  general  illumination  sufficient  without  their  use. 

(4)  The  blinding  effect  of  bright  rays,  commonly  called  glare, 
should  be  reduced  to  a  minimum  through  a  proper  arrangement 
of  the  lamps,  and  by  the  use  of  a  suitable  size  of  lamp  and  a 
suitable  reflector. 

(5)  Steadiness   of  the   light   should   be   secured   by   constant 
voltage;  that  is,  the  lamps  should  not  flicker  with  the  varying 
demands  on  lighting  circuits. 

(6)  Adaptation  to  Conditions. — The  type  of  lamp  should  be 
selected  in  reference  to  the  foregoing  requirements  and  to  the 
particular  class  of  work  to  be  served;  also  to  the  limitations  of 
mounting  height,  and  the  general  physical  surroundings,  such 
as  the  clearance  between  cranes  and  ceiling. 

3.  Classification. — Factory    lighting   may    be    classified    into 
two  general  divisions:  first,   general  illumination  provided  by 
lamps   mounted   over-head;    and   second,    specific   illumination 
provided  by  individual  lamps  located  close  to  the  work.     For 
practical  purposes  this  classification  is  sufficient.     In  numerous 


GENERAL  ITEMS  AND  REQUIREMENTS  3 

cases  a  combination  of  these  two  methods  must  be  used,  but 
further  subdivision  is  hardly  necessary. 

General  Lighting. — Where  the  lamps  are  high  enough  to  be 
out  of  the  line  of  ordinary  vision,  and  are  of  a  size  and  are  so 
spaced  as  to  furnish  illumination  at  any  position  of  the  floor 
where  work  may  be  placed,  the  system  is  referred  to  as  the  over- 
head method  of  lighting.  This  method  has  many  advantages 
which  will  be  subsequently  outlined.  Its  general  adoption, 
which  has  been  somewhat  slow,  has  increased  with  the  intro- 
duction of  the  many  new  types  of  lamps. 

Specific  Lighting. — Where  a  small  amount  of  general  illu- 
mination from  over-head  lamps  is  coupled  with  specific  illumina- 
tion from  individual  lamps,  a  large  part  of  the  floor  space  in 
many  shops  is  in  relative  darkness,  and  much  dependence  must 
be  placed  on  the  hand  lamps  close  to  the  work.  The  small 
number  of  over-head  lamps  generally  used  in  such  cases  pro- 
vides merely  a  small  amount  of  additional  illumination  over  the 
floor  space. 

Locations  with  low  ceilings,  until  recently,  have  been  lighted 
by  the  individual  hand  lamp  method,  because  the  carbon-fila- 
ment lamp,  being  of  low  candle-power,  could  not  well  be  used 
close  to  the  ceiling,  while  the  old  type  of  arc  lamp  was  often 
impractical,  due  to  its  large  physical  size,  as  well  as  its  relatively 
high  candle-power.  This  statement  must  be  slightly  modified 
as  carbon-filament  lamps  have  sometimes  been  used  in  clusters 
for  low  ceilings,  this  scheme  being,  however,  inefficient  and  un- 
satisfactory in  comparison  with  modern  methods  of  lighting. 
In  a  particular  manner,  therefore,  suitable  illumination  has 
been  difficult  with  low  ceilings. 

New  types  of  lamps  have  a  range  of  candle-power  from  very 
low  to  very  high  values,  and  the  over-head  system  with  the 
elimination  of  hand  lamps  is  thus  possible;  that  is,  a  size  of  lamp 
may  now  be  selected  for  nearly  every  factory  condition. 

4.  The  Influence  of  Candle-power  and  Physical  Dimensions 
of  Modern  Lamps. — The  development  of  electric  lamps  has  con- 
sisted, first,  in  increased  candle-power  for  given  power  consumed; 
and  second,  in  the  tendency  toward  a  reduction  in  physical  di- 
mensions for  given  candle-power  values.  Notable  results  have 
been  attained  in  these  directions.  The  illumination  in  previous 
years,  mainly  by  the  carbon-filament  lamp  and  the  arc  lamp, 
is  now  produced  by  a  diversity  of  lamp  sizes.  The  old  carbon- 


4  FACTORY  LIGHTING 

filament  lamp  as  one  extreme  has  been  followed  by  the 
metallized  filament,  the  tantalum  and  the  tungsten  lamp;  and 
the  old  open  arc  lamp  as  the  other  extreme,  by  the  enclosed 
carbon  arc,  the  open  flame  carbon  arc,  the  metallic  flame  or 
magnetite  arc,  and  the  long-burning  flame  carbon  arc  lamp. 
In  addition,  other  lamps,  as  previously  intimated,  are  now 
available,  namely,  the  Nernst,  the  mercury  vapor,  the  quartz 
mercury  vapor,  and  the  Moore  tube  lamps. 

The  limitations  in  candle-power  of  old  as  compared  to  new 
lamps  are  shown  in  Fig.  1.  The  average  mean  spherical  candle- 
power  values  of  old  as  well  as  new  types  are  taken  from  various 


Carbon 
Filament 

Enclosed 
Carbon  Arc 

Open  Carbon 
Arc 

New  Types 
Tungsten 

Nernst 
Mercury  Vapor 

Quartz  Mercury 
Vapor 

Metallic  Flame 
Arc 

Flame  Carbon 
Arc 

8 

| 

—  ~ 

w< 

•:••:•:••••• 

:.-'.' 

- 

w 

w 

••".'.' 
•:••  ••:• 

\ 

w 

~W. 

x?j 

P 

M 

•:•:-•  :  " 

M 

:    ' 

.  ••: 

<:::::::;;:;v:::xXv>} 

'.'.'.'.' 

VT-T- 

-™ 

rV-'-'. 

••v.v.. 

$?TW 

200        400        600        800        1000      1200      1400       1600 
Mean  Spherical  Candle- Power  Ranges 

FIG.  1. — Candle-power  ranges  of  relatively  old  and  new  lamps. 

authorities.  The  chart  shows  further  that  the  new  lamps  not 
only  have  candle-power  values  between  those  of  former  years, 
but  also  far  greater  values  than  were  available  in  the  past. 

The  physical  dimensions  of  lamps  are  important  in  factory 
work  owing  to  the  difficulty  in  the  installing  of  lamps  in  many 
locations.  The  small  clearance  between  cranes  and  ceiling, 
and  other  limiting  conditions,  often  make  the  over-all  dimensions 
a  determining  factor.  The  relative  over-all  dimensions  of  va- 
rious old  and  new  types  are  shown  in  Fig.  2. 

5.  Effective  Illumination. — High  candle-power  per  watt  power 
input  is  but  one  method  of  obtaining  effectiveness  from  electric 
lamps.  Many  lamps  would  be  very  inefficient  in  the  illumi- 


GENERAL  ITEMS  AND  REQUIREMENTS  5 

nation  they  furnish  were  it  not  for  reflectors.  The  rays  of  light 
otherwise  dissipated  in  horizontal  or  upward  directions  are 
thus  sent  mainly  in  useful  downward  directions. 

Electric   lighting   systems   are   now  rated   according   to   the 
effective  intensity  of  illumination  on  the  work  rather  than  the 


FIG.  2. — Over-all  dimension  shown  in  comparative  manner  of  relatively  old 

and  new  lamps. 

quantity  of  light  produced  by  the  lamps,  the  question  now  being 
that  of  illumination  as  well  as  light  efficiency. 

6.  Quality  of  Light  and  Illumination. — Electric  lamps  are  made 
to-day  not  only  in  a  large  variety  of  sizes  but  also  with  various 
qualities  of  light.  The  criterion  of  good  light  has  usually,  in 
the  past,  been  quantity;  quality  is  now  almost  on  a  par  with 
quantity. 

The  quality  of  the  light  includes  principally  its  color  value, 
while  the  quality  of  the  illumination  relates  to  such  items  as  uni- 
formity over  the  working  area,  diffusion,  adequate  intensities  on 
the  sides  of  the  work,  absence  of  glare,  and  the  like.  These 
items  are  of  equal,  or  greater  importance  than  the  securing 
of  a  definite  downward  intensity  of  the  illumination.  Refine- 
ments in  the  quality  of  illumination,  as  well  as  certain  standards 
with  reference  to  quantity  in  relation  to  factory  conditions,  and 
the  significance  of  these  factors  in  manufacturing  efficiency 
will  be  indicated  under  appropriate  heads. 


CHAPTER  II 
ILLUMINATION  DESIGN 

7.  Scope  of  Illumination  Design. — Illumination  design  refers 
to  the  preparation  of  plans  and  specifications  for  lighting  sys- 
tems, in  the  determination  of  the  best  available  type  of  lamp 
for  the  location  it  is  to  serve,  and  in  the  indication  of  how  such 
lamps  are  to  be  placed.     This  work  obviously  covers  a  large 
variety  of  problems  and  the  steps  for  a  given  case  may  be  stated 
as  follows: 

(1)  The  determination,  through  a  study  of  the  requirements 
and  the   surroundings,    of  the   quantity   and  quality   of  light 
necessary. 

(2)  The  study  of  how  the  light  can  best  be  provided. 
Under  the  latter  head  a  selection  is  made  in  a  scientific  and 

practical  manner  of  (a)  the  type;  (b)  the  size;  and  (c)  the  number 
of  lamps  required;  together  with  (d)  their  spacing;  and  (e) 
their  mounting.  From  these  items  proper  plans  may  be  provided 
for  attaining  desired  results. 

8.  Inspection  of  the  Location. — The  first  step  in  the  design 
is  to  ascertain,  by  inspection  or  otherwise,  the  class  of  work  in- 
volved.    This  largely  determines  the  intensity  of  illumination 
necessary  for  satisfactory  conditions,   and  also,  in  a  measure, 
the  number  of  lamps  to  be  used. 

The  dimensions  of  the  location  should  be  measured,  since 
the  width,  length  and  height  determine  in  general  the  total  num- 
ber of  lamps  necessary,  as  well  as  the  character  of  the  area  over 
which  the  lamps  are  to  be  distributed. 

The  location  and  size  of  columns,  when  present,  dividing  as 
they  do  the  floor  space  into  bays  of  a  certain  number  and  size, 
should  be  noted;  the  class  of  ceiling,  whether  plain  or  set  with 
deep  girders,  in  their  relation  to  symmetry  and  convenience  of  the 
wiring;  and  the  color  of  ceiling  and  walls,  whether  light  or  dark, 
in  its  effect  as  an  aid  to  the  rays  of  light  transmitted  directly 
to  the  work,  as  the  extra  light  from  the  reflection  of  rays  trans- 
mitted directly  to  the  ceiling  and  walls  and  thence  reflected  to 
the  floor,  is  often  a  large  factor. 

6 


ILLUMINATION  DESIGN  7 

The  girders,  when  present,  should  further  be  observed,  both 
regarding  height  and  location,  in  that  very  deep  girders  may 
cause  appreciable  shadow  effects  where  the  lamps  must  be 
mounted  near  the  ceiling.  The  type  of  wall  has  a  bearing,  first, 
on  the  locating  of  the  control  circuits  and  switches,  and  second, 
in  the  matter  of  color  in  its  reflecting  power,  either  as  an  aid  to 
the  net  illumination,  or  perhaps  in  the  blinding  effect  or  glare 
sometimes  caused  when  looking  at  brightly  lighted  walls,  a  fea- 
ture most  noticeable,  of  course,  in  the  case  of  glossy  light  colors, 
and  where  too  much  light  shines  on  the  walls. 

Where  the  space  to  be  lighted  is  merely  a  portion  of  a  large  floor 
area  divided  from  the  other  portions  of  the  building  by  columns, 
the  switches  must  in  general  be  mounted  on  the  columns,  and 
the  surroundings  treated  as  dark  walls  as  far  as  reflection  is 
concerned,  unless  the  lamps  in  the  surrounding  floor  space 
contribute  light  to  the  space  in  question. 

The  Supply  Circuits. — The  electric  circuits  contemplated 
in  the  case  of  new  plants,  or  those  available  in  old  plants, 
must  be  noted  as  to  capacity  of  the  wires;  the  voltage  and 
its  variation  dependent  upon  variable  power  requirements; 
and  whether  direct  or  alternating  current  is  to  be  used  for 
lighting.  The  importance  of  these  items  will  be  apparent  when 
it  is  considered  that  the  type  of  lamp  is  thus  largely  influenced. 
Table  I  indicates  the  classes  of  circuits  commonly  used  in  indus- 
trial plants  and  the  types  of  lamps  which  are  available  for  each. 

The  Space  between  Floor  and  Ceiling. — The  conditions  of  the 
free  space  between  the  work  and  the  ceiling  should  be  noted. 
Under  this  head  is  included  open  locations  free  from  belting; 
spaces  filled  with  many  belts;  and  those  in  which  much  dust  and 
dirt  is  present  in  large  quantities,  as  for  example  in  the  foundry. 

Daylight  Conditions. — The  natural  lighting  facilities  should 
be  observed  in  that  the  switch  control  of  lamps,  generally  ar- 
ranged in  rows  or  groups  parallel  to  the  windows,  is  thus  largely 
dependent  on  the  location  of  windows.  It  should  also  be  stated 
that  the  required  intensity  of  artificial  light  when  necessary 
at  certain  portions  of  the  day  due  to  clouds  or  smoke,  is  some- 
what dependent  in  such  cases  on  the  amount  of  natural  light 
present.  Under  mixed  conditions  of  natural  and  artificial  light, 
the  artificial  light,  to  be  satisfactory,  must  usually  have  a  higher 
intensity  than  would  be  the  case  if  its  use  was  limited  to  the  hours 
of  total  darkness. 


FACTORY  LIGHTING 


TABLE  I. — ELECTRIC  CIRCUITS  ORDINARILY  FOUND  IN  PRACTICE  AND 
TYPES  OF  LAMPS  OPERATIVE  THEREON 

Direct-current  circuits 


Series 

Multiple  or  multiple  series 

110  volts 

220  volts 

550  volts 

Carbon  filament. 
Gem. 
Tungsten. 
Enclosed  carbon 

Carbon  filament. 
Gem. 
Tungsten. 
Enclosed  carbon 

Carbon  filament. 
Gem. 
Tungsten. 
Enclosed  carbon 

Carbon  filament. 
Gem. 
Tungsten. 
Enclosed  carbon 

arc. 
Metallic  flame 

arc. 
Metallic  flame 

arc. 
Metallic  flame 

arc. 
Metallic  flame 

arc. 
Flame  carbon 

arc. 
Flame  carbon 

arc. 
Flame  carbon 

arc. 
Flame  carbon 

arc. 

arc. 
Nernst. 
Cooper-Hewitt. 

arc. 
Nernst. 
Cooper-Hewitt. 

arc. 
Cooper-Hewitt. 

Alternating-current  circuits 


Series 

Multiple 

110  volts 

220  volts 

25  cycles 

60  cycles 

25  cycles            60  cycles 

Carbon  fila- 

Carbon fila- 

Carbon fila- 

Carbon fila- 

Carbon fila- 

ment. 

ment. 

ment. 

ment. 

ment. 

Gem. 

Gem. 

Gem. 

Gem. 

Gem. 

Tungsten. 

Tungsten. 

Tungsten. 

Tungsten. 

Tungsten. 

Enclosed   car- 

Flame carbon 

Enclosed  car- 

Flame car- 

Enclosed 

bon  arc. 

arc  (long 

bon  arc. 

bon  arc  (long 

carbon  arc. 

burning)  . 

burning). 

Flame  carbon 

Flame  carbon 

Flame  carbon 

arc. 

arc. 

arc. 

Nernst. 

Nernst. 

Nernst. 

Nernst. 

Cooper- 

Cooper- 

Hewitt. 

Hewitt. 

Thus  on  a  cloudy  day,  when  natural  illumination  is  insufficient, 
a  greater  intensity  of  the  added  artificial  light  is  necessary  to 
produce  satisfaction  for  the  eye  than  on  the  same  work  at  night. 
This  is  probably  best  explained  by  considering  that  the  eye  is 
contracted  during  the  day  on  account  of  the  relatively  great 
intensities  of  daylight  as  compared  to  artificial  light.  In  this 
contracted  state  the  eye  is  not  as  sensitive  to  changes  in  illumi- 
nation intensity  as  at  night  when  relaxed  under  the  relatively 
low  intensities  of  artificial  light. 

If,  therefore,  the  lighting  system  has  been  designed  for  an 
intensity  suitable  at  night,  it  is  possible  that  the  intensity  of 
this  same  system  may  not  be  adequate  at  those  times  during 


ILLUMINATION  DESIGN  9 

the  day  when  required.  Hence  an  allowance  is  sometimes  made 
in  the  design  for  the  difference  between  day  and  night 
requirements. 

9.  Reflectors  and  Globes. — A  reflector  is  used  in  conjunction 
with  a  lamp  for  the  purpose  of  reducing  the  glare  otherwise  caused 
by  looking  directly  into  a  bare  lamp,  as  well  as  for  the  purpose  of 
redirecting  the  light  most  effectively  to  the  work. 

Uniformity  of  Illumination. — Reflectors  are  now  obtainable 
which  are  designed  for  specific  sizes  of  lamps,  and  hence  care 
should  be  used  to  be  sure  that  both  reflectors  and  lamps  are  of 
the  correct  size  in  their  relation  to  each  other.  This  is  of  the 
utmost  importance  in  securing  uniform  illumination  for  a  given 
spacing  distance  and  mounting  height  of  the  lamps.  For  a 
certain  ratio  between  the  spacing  and  height  of  lamps,  a  reflector 
can  nearly  always  be  secured  which  will  furnish  uniform  il- 
lumination on  the  working  plane.1 

Redirection  of  Light. — Owing  to  the  direction  of  the  light 
rays  from  the  lamp,  nearly  all  types  of  lamps,  in  addition  to  down- 
ward light,  furnish  some  rays  which  go  upward  or  away  from 
the  objects  to  be  illuminated,  and  are  therefore  relatively  not 
useful.  The  function  of  a  reflector  is  to  intercept  these  other- 
wise useless  or  comparatively  useless  rays  and  reflect  them  in 
a  useful  direction.  In  performing  this  function  there  is  a  choice, 
through  the  design  of  the  reflector,  in  the  manner  of  distributing 
the  light  so  as  to  make  the  illumination  on  the  floor  space  prac- 
tically uniform  with  certain  spacing  distances  and  mounting 
heights. 

With  the  use  of  lamps,  like  the  tungsten  type,  for  which  a 
large  variety  of  reflectors  is  available,  the  proper  reflector  for 
the  given  spacing  distance  and  mounting  height  must  be 
selected  if  uniform  illumination  on  the  floor  is  to  be  obtained. 
In  other  cases,  as  in  the  use  of  the  arc  lamp,  where  the  globe 
or  reflector  is  usually  a  fixed  part  of  the  lamp,  care  must  be 
exercised  to  space  the  lamps  at  sufficiently  close  intervals  to 
insure  uniformity  of  the  illumination,  that  is,  a  freedom  from  the 
relatively  dark  spaces  which  exist  between  lamps  when  spaced 
too  far  apart.2 

1  This  statement  applies  more  especially  to  tungsten  lamps  than  to  other 
types. 

2  The  Holophane  Company  (now  known  as  the  Holophane  Works  of  the 
General  Electric  Company,  Cleveland,  Ohio)  has  designed  and  placed  on  the 


10  FACTORY  LIGHTING 

10.  Type  of  Lamp. — The  choice  of  type  of  lamp  is  dependent 
upon  several  items,  chief  of  which  are  the  electric  supply  avail- 
able, space  conditions,  to  some  extent  on  the  element  of  color 
of  the  light  produced,  the  surroundings,  the  limits  of  candle- 
power  values  of  the  different  lamps  of  a  given  type,  and  upon 
the  cost  of  operation. 

The  surroundings  have  a  considerable  influence  on  the  type 
of  lamp  to  be  used.  Obviously  arc  lamps  would  not  be  used 
in  a  small  office,  nor  would  it  be  advantageous  to  use  small 
tungsten  lamps  in  very  high  factory  spaces.  The  condition  of 
the  space  between  floor  and  ceiling,  that  is,  whether  or  not  there 
is  much  belting,  will  also  often  determine  the  type  of  lamp, 
for  it  has  been  found  by  experience  that  where  much  belting 
exists,  lamps  of  the  mercury  vapor  type,  for  example,  are  more 
advantageous  than  those  units  which  furnish  the  light  from  a 
point  rather  than  from  a  long  tube. 

Often  the  size  of  lamp  desired  is  either  of  a  very  small  or  a 
very  large  candle-power,  and  this  leads  to  the  choice  of  that  type 
of  lamp,  which  possesses  the  required  volume  of  light.  Again, 
some  lamps  are  best  adapted  to  alternating  current  and  others 
to  direct-current  circuits;  some  must  be  operated  in  series 
and  others  in  multiple;  hence  the  characteristics  of  the  circuit 
on  which  the  lamps  are  to  be  operated  will  largely  determine 
the  choice,  although  110-volt  direct-current  or  alternating-current 
circuits  cover  practically  all  cases. 

The  relative  first  cost  and  operation  cost  of  the  various  lamps 
are  items  of  considerable  weight  in  the  choice  between  one  or 
another  type,  and  these  items  will  be  discussed  in  connection  with 
the  specific  lighting  appropriate  to  various  departments  of  the 
factory. 

11.  Size  of  Lamp. — The  proper  size  of  lamp  for  a  given  loca- 

market  a  standard  line  of  reflectors  for  tungsten  lamps  calculated  to  furnish 
uniform  illumination  on  the  working  surface  provided  the  ratio  between 
spacing  distance  and  mounting  height  is  in  accord  with  the  conditions  for 
which  the  reflector  was  designed.  This  standard  line  consists  of  the  focus- 
ing type,  concentrating;  the  intensive  type,  moderately  distributing;  and 
the  extensive  type,  broadly  distributing.  The  focusing  type  is  intended  for 
use  where  the  ratio  of  spacing  to  mounting  height  is  about  0.7;  the  intensive 
type  where  this  ratio  is  about  1.25;  and  the  extensive  type  where  this  ratio 
is  about  2.0.  Reflectors  of  other  manufacturers  may  be  used  to  furnish 
similar  results  provided  their  distribution  conforms  in  a  general  way  to  the 
distribution  of  the  reflectors  referred  to. 


ILLUMINATION  DESIGN 


11 


tion  is  dependent  on  the  spacing  decided  upon.  The  size  of 
lamp  for  a  system  should,  however,  primarily  be  based  on  the 
height  of  mounting.  Fig.  3  shows  that  for  a  given  shadow  effect, 
the  lower  the  ceiling  the  smaller  may  be  the  size  of  lamp  because 
of  the  closer  spacing.  In  like  manner,  for  high  ceilings,,  larger 
lamps  with  wider  spacing  may  be  used.  Furthermore,  the  fatigue 
of  the  eyes  is  less  with  small  lamps,  if  they  must  be  mounted  low. 


FIG.  3. — Relation  of  shadow  effect  to  average  spacing  and  mounting  height 

of  lamps. 


Experiment  and  experience  determine  the  relation  between 
mounting  height  and  candle-power,  and  this  solution  can  hardly 
be  realized  through  any  "other  channel.  Table  II  has  been 
prepared  to  show  candle-power  sizes  which  have  been  used  in  a 
variety  of  factory  locations  for  various  mounting  heights,  and 
a  reference  to  this  table  will  indicate  that  for  low  ceilings  small 
lamps  are  generally  selected  in  well  designed  installations, 
the  sizes  increasing  with  the  height. 


12 


FACTORY  LIGHTING 


TABLE  II. — CANDLE-POWER   OF  LAMPS   CORRESPONDING   TO    MOUNTING 
HEIGHT  AS  RECOMMENDED  FROM  THE  EXPERIENCE  OF  THE 

AUTHOR  FOR  DISTRIBUTED  LIGHTING  SYSTEMS 
This  table  is  suggestive  only,  as  fixed  rules  may  mislead 


Mounting  height 
in  feet 

Candle-power 
of  lamp 

Corresponding  lamp  type  or  types 

9  to  12 

48  to  80 

Tungsten  60  and  100  watt. 

12  to  16 

80  to  300 

Tungsten  100,  150  and  250  watt;  mer- 

cury vapor  and  in   certain  cases   arc 

lamps. 

16  to  25 

200  to  500 

Tungsten  250,  400  and  500  watt;  mer- 

cury vapor  and  arc  lamps. 

25  to  50 

300  to  3,000 

Tungsten  400  and  500  watt;  mercury 

vapor;  quartz  and  arc  lamps. 

Note.  —  Small  lamps  are  in  general  preferable  to  large  ones,  and  when 
there  is  a  range  to  choose  from,  it  is  advisable  to  lean  to  the  smaller  rather 
than  the  larger  from  the  illumination  standpoint. 

12.  Spacing  of  Lamps.—  The  spacing  distances  will  largely 
depend  on  the  condition  of  the  work,  whether  crowded  or  scat- 
tered over  a  given  floor  area,  and  also  to  some  extent  on  whether 
the  work  must  be  viewed  from  the  side  as  well  as  from  above. 
Further,  the  spacing  is  naturally  dependent  on  the  size  of  the 


TABLE  III.  —  SPACING  DISTANCES  FOR  TUNGSTEN  LAMPS,  OR  LAMPS 
EQUIVALENT  CANDLE-POWER,  RECOMMENDED  FROM  THE  EXPERI- 
ENCE OF  THE  AUTHOR  FOR  DISTRIBUTED  LIGHTING  SYSTEMS 
This  table  is  suggestive  only,  as  fixed  rules  may  mislead 


OF 


Ceiling  height 
in  feet 

Location 

Spacing  distance 

9  to  12 

Office. 

6ft.  0  in.  to    7ft.  6  in. 

12  to  16 

Office. 

7ft.  6  in.  to    9ft.  0  in. 

9  to  16 

Drafting  rooms.1 

8  ft.  0  in.  to    9  ft.  6  in. 

9  to  12 

Factory,    power-house    and     steel 

8  ft.  0  in.  to  10  ft.  0  in. 

mills. 

12  to  16 

Factory,    power-house     and    steel 

10ft.  0  in.  to  12ft.  0  in. 

mills. 

16  to  25 

Factory,    power-house     and     steel 

12  ft.  0  in.  to  15  ft.  0  in. 

mills. 

25  to  50 

Factory,    power-house     and    steel 

(Spacing  depends  large- 

mills. 

ly  on  circumstances.) 

Note. — Tables  II,  III  and  IV  are  intended  for  use  together.  Obviously 
the  size  of  lamp  cannot  be  determined  from  this  table,  but  must  be  selected 
from  Table  II.  Table  IV  is  a  check  on  the  selection  of  size  and  spacing 
distance. 


1  The  spacing  here  given  refers  to  the  inverted  fixture  or  semi-direct  light- 
ing scheme  as  shown  in  Fig.  62. 


ILLUMINATION  DESIGN  13 

lamp,  that  is,  for  a  given  size  of  lamp,  a  given  spacing  is  necessary 
in  order  to  produce  the  required  amount  of  illumination.  Hav- 
ing determined  the  approximate  size  of  lamp  for  the  height  of 
the  location,  the  advisable  spacing  distance  may  in  turn  be 
determined  independently,  based  on  the  nature  of  the  work  and 
its  disposition  over  the  floor  space.  The  size  of  lamp  and  the 
spacing  distance  for  the  system  should  then  be  brought  together, 
that  is,  adjusted  to  each  other,  to  produce  the  desired  intensity. 
Table  III  shows  average  spacing  distances  for  a  variety  of  in- 
dustrial conditions,  referring  mainly  to  tungsten  lamps  or  other 
types  of  equal  candle-power. 

13.  Mounting  Height  of  Lamps. — The  mounting  height  of 
lamps  is  often  limited  by  the  details  of  building  construction  or 
by  the  interference  of  cranes.  In  general,  the  lamps  should  be 
mounted  at  such  a  height  as  to  be  out  of  the  line  of  vision,  thus 
preventing  that  glare,  or  blinding  effect,  which  results  from  look- 
ing directly  into  lamps  mounted  too  low/ 

Where,  however,  the  ceiling  itself  is  low,  ,thus  limiting  the 
available  mounting  height,  small  lamps  properly  equipped 
with  reflectors  should  be  used.  Thus  the  system  is  not  as  likely 
to  produce  fatiguing  effect  on  the  eye  as  if  large  lamps  are  in- 
stalled. The  glare  and  resulting  eye  fatigue  and  even  strain 
from  lamps  mounted  low  enough  to  be  in  the  line  of  vision  is 
extremely  harmful,  and  in  addition  to  the  evil  effect  on  the 
eye,  it  renders  the  resulting  illumination  less  effective.  The 
contraction  of  the  pupil  under  the  stimulus  of  the  bright  lamp 
causes  the  eye  to  be  less  responsive  than  otherwise. 

Sometimes  it  is  necessary  that  the  light  from  over-head  lamps 
shall  fall  upon  the  work  at  an  angle,  as  in  the  case  of  work  in  a 
vise  or  in  a  milling  machine.  In  such  cases  it  may  be  necessary 
to  mount  the  lamps  lower  than  would  be  advisable  were  glare 
the  only  consideration.  In  the  production  of  a  greater  side 
component  of  the  light  it  is  usually  better,  however,  to  keep 
the  lamps  high  and  to  provide  them  with  broader  distributing 
reflectors  than  would  be  called  for  by  rules  looking  merely  to 
uniform  downward  illumination,  thus  securing  sufficient  side 
ilght  without  the  objectionable  glare. 

The  mounting  height,  although  partially  fixing  the  size  of 
the  lamp  to  be  used,  should  be  determined  with  exactness  after 
the  spacing  has  been  fixed.  The  determination  of  mounting 
height  should  be  such  as  to  secure  uniformity  of  the  resulting 


14  FACTORY  LIGHTING 

illumination,  provided  glare  is  not  incurred  by  too  low  a  mount- 
ing as  an  extreme  case.  With  Holophane  prismatic  reflectors  the 
proper  height  is  determined  by  the  ratio  of  spacing  distance  to 
mounting,  for  which  a  given  type  of  reflector  has  been  designed 
so  as  to  furnish  uniform  results  as  already  described  in  Art.  9. 
The  proper  mounting  height  for  uniform  or  nearly  uniform  dis- 
tribution may  be  determined  for  all  types  of  lamps,  provided  the 
distribution  curve  of  the  particular  type  of  lamp  in  question  is 
available.  This  calculation,  although  somewhat  tedious,  may  be 
made  as  described  under  the  subject  of  point  addition  in  Art.  17. 

14.  Switch  Control. — The  control  of  lamps  in  industrial 
lighting  systems  is  important  in  all  cases,  but  more  especially 
where  a  large  number  is  used  in  preference  to  a  small  number 
of  lamps  for  given  factory  spaces.  For  example,  where  tungsten 
lamps  of  small  size  are  used,  a  large  number  will  of  course  be 
necessary  for  given  floor  areas,  and  in  such  cases  the  number 
of  control  circuits  may  at  times  seem  excessive.  Such  circuits, 
however,  in  rendering  the  system  more  flexible,  will  be  more 
than  paid  for  by  the  saving  in  energy  and  maintenance  due 
to  turning  out  lamps  not  needed  in  certain  sections  of  the  fac- 
tory, provided  the  number  of  hours  per  day  the  lamps  are  used 
on  the  average  is  relatively  large. 

The  lamps  most  distant  from  the  windows  will  usually  be  re- 
quired at  times  when  the  natural  light  near  the  windows  is  en- 
tirely adequate,  thus  making  it  an  advantage  to  arrange  the 
groups  of  lamps  in  circuits  parallel  to  the  windows.  This 
scheme  is  shown  in  Fig.  4.  The  advantage  of  this  method  is 
further  apparent  when  it  is  considered  that  if  lamps  are  controlled 
in  rows  perpendicular  to  the  windows,  all  lamps  in  a  row  will 
necessarily  be  on  at  one  time,  while  a  portion  only  may  be 
required. 

The  foregoing  statement  may  be  developed  into  a  simple 
proposition.  To  install  a  single  switch  may  involve  say  $5.00 
as  the  first  cost.  If  ten  60-watt  tungsten  lamps  are  to  be  con- 
trolled from  a  single  switch,  these  ten  lamps  must  obviously 
either  all  be  turned  on  or  off.  An  additional  switch  at  a  cost 
of  $5.00  will  permit  either  half  of  these  ten  lamps  being  turned 
off,  if  not  required,  while  the  remaining  five  are  needed.  This 
extra  switch  may  or  may  not  be  an  economy.  Consider,  for 
example,  the  case  where  these  five  60-watt  tungsten  lamps  are 
turned  off  by  the  extra  switch  on  an  average  of  one-half  hour 


ILLUMINATION  DESIGN 


15 


per  day  while  the  others  are  needed,  or  vice  versa.  In  a  year's 
time  the  energy  saved  at  1  cent  per  kilowatt-hour  will  amount  to 
perhaps  50  cents.  At  this  rate  it  will  require  ten  years  for  the 
energy  saved  to  pay  for  the  first  cost  of  the  extra  switch.  Natur- 
ally this  would  not  be  a  distinct  economy.  If  the  energy  cost  be 
greater,  or  if  the  number  of  hours  per  day  during  which  a  portion 
only  of  the  lamps  will  not  be  used  be  greater,  these  values  will 
of  course  be  correspondingly  modified. 


^$$$}—  K$$$ 

ssssi—  —  R$$$ 

J$$$$j  ^$$$^$$$$$1  —  •  R$$$ 

:;$$$^  ^ 

$$$$$^  £$$$$: 

'K-4>!  Ki 

[K  "~K] 

[k      kl 

TO  rji 

i  tf          XC  i 

TK       kl 

-44^8^4-4- 

^  ft-  —  ~^TJ 

1  [3t""J  E 

[K        Kj 
i 

i 
j 

[K  KJ 

«         Kj 

^,.J 

fk      •«! 
i 
i 
i           i 

!K  _K] 

I                            F 

["K      KI 

i"i 

ta       »| 

J=T-=-J 

P     3        L 

j       '        [ 

J                          L 

J                          L 

r  ,-  -  .,  i 

•Pf    1 

!    ? 

«4  '« 

i 

L^T    ^ 

|K      KJ 

«         KJ 

1 
uK  KJ 
i                    F 

K         Kj 
i 

K         Kj 

,  &*  , 

XC         K1 

i 
i                j 

,  Is-d 

f«      w] 

1                   1 

«      « 

1                    i 
j                    i 

L  *=#  J 

JK      k1 

| 

!K      K 
i 
i 
i 

[K_  _K 

]  T  1 

J                          L 

J                          L 

jW^     K 

!   "°p 

lK-f-     K1 

«         Kj 

i 

j  A           A| 

1                   i 
i                   i 

i  )^(           KI 

K         Kj 

i               i 
i                i 

!K      KJ 

IK      K] 

!       ! 

!K         Kj 

JK      « 
!«       KJ 

^ 

[K-pN    Kj 

fa      kl 

[K         W^ 

[k      KJ 

iW          X(j 

L«  K] 

k^i  t^mi  i^^  {^ 

^^         K^ 

^a  fe^ 

^a  (^ 

Plan 


*I;;:!:^^W^:^:>:SN^^ 

Elevation 
FIG.  4. — Switch  control  shown  parallel  to  windows.     (See  also  Fig.  24.) 

15.  The  Working  Drawing.— After  the  spacing  of  the  lamps 
has  been  decided  upon,  the  next  step  will  be  to  indicate  the  ar- 
rangement on  a  diagram  drawing  of  the  floor  space  as  shown 
in  Fig.  4.  This  plan  should  contain  an  elevation,  where  such  an 
addition  to  the  drawing  will  make  it  more  intelligible.  The 
drawing,  to  be  of  practical  service,  should  contain  the  floor 


16  FACTORY  LIGHTING 

space  outline  drawn  accurately  to  scale  with  the  columns  located 
in  such  a  manner  as  to  be  easily  identified.  In  the  case  of  new 
buildings  the  framing  plan  showing  the  exact  location  of  the  iron 
work  is  useful.  Further,  the  lamps  should  be  located  to  scale 
and  all  spacing  distances  given,  the  dimensions  to  be  referred 
to  some  point  on  structural  columns  or  other  boundary  locations. 

The  scale  of  the  drawing  is  of  some  importance,  due  to  the  fact 
that  too  small  a  scale  may  make  an  interpretation  of  the  design 
difficult  for  the  wiremen  when  making  the  installation.  In 
general,  1/4  or  1/8  in.  to  the  foot  will  be  found  convenient. 

On  the  drawing  the  arrangement  of  switch  circuits  may  be 
shown  by  placing  a  numeral  adjacent  to  each  lamp.  Thus,  if 
four  given  lamps  are  to  be  controlled  from  one  switch,  the  nu- 
meral (l)  adjacent  to  each  of  these  four  lamps  will  indicate  the 
fact.  This  feature  is  shown  in  Fig.  24.  Another  simple  method 
is  to  surround  all  lamps  to  be  controlled  from  one  switch  by  a 
dotted  line,  as  shown  in  Fig.  4. 

The  drawing  should  also  contain  or  be  accompanied  by  specifi- 
cations, including  the  type  of  lamp,  reflector  and  reflector  holder, 
the  mounting  height  of  the  lamps  and  such  other  details  as  may 
be  necessary  for  the  one  who  is  to  order  the  supplies,  or  for  the 
wiremen  who  have  the  installation  in  hand. 

16.  Lighting  System  Efficiency.— The  ratio  of  the  actual 
light  which  is  received  by  the  work  to  the  total  light  given  out  by 
the  lamps  is  here  defined  as  the  efficiency  of  the  lighting  system. 
This  ratio  must  be  obtained  by  the  use  of  the  proper  units  of 
light,  usually  expressed  in  terms  of  the  light  flux  furnished  to  the 
work,  divided  by  the  total  light  flux  from  the  lamps.1 

The  calculation  of  the  total  number  of  lamps  necessary  for 
lighting  a  location  could  be  based  on  the  efficiency  predicted 
for  the  conditions  of  the  given  location.  Thus,  based  on  tests 

1  The  term  flux  is  used  to  express  the  total  quantity  of  light  either  given 
by  the  lamp,  or  incident  to  a  given  surface.  For  example,  a  60-watt  tungsten 
lamp  at  a  certain  rating  develops  say  500  lumens  or  in  other  words  500  units 
of  light  flux.  Thus,  if  out  of  a  total  of  500  lumens  but  100  are  effective  on 
the  working  surfaces,  the  other  400  being  wasted  in  directions  not  useful  to 
the  work  and  absorbed  by  dark  surroundings,  the  system  is  said  to  have  an 
efficiency  of  100  divided  by  500,  or  20  per  cent.  This  method  of  calculating 
efficiency  obviously  takes  into  account  the  condition  of  surroundings  as  well 
as  the  lighting  units.  The  lumen  value  here  taken  for  a  60-watt  tungsten 
lamp  is  not  a  fixed  quantity,  but  depends  altogether  on  the  watts  consump- 
tion per  candle-power  at  which  the  lamp  is  operated. 


ILLUMINATION  DESIGN  17 

in  other  similar  locations,  the  illumination  efficiency  in  a  typical 
factory  location  might  be  predicted  to  equal  25  per  cent.  If 
an  illumination  intensity  of  three  foot-candles1  on  the  work 
is  desired,  the  total  light  flux  in  lumens  is  found  by  the  product 
of  the  floor  space  in  square  feet  and  the  intensity  of  the  illu- 
mination in  foot-candles.  This  result  divided  by  the  predicted 
efficiency  is  equal  to  the  total  light  flux  which  must  be  furnished 
by  the  entire  number  of  lamps  in  the  proposed  system. 

On  the  other  hand,  the  importance  of  choosing  the  proper 
size  of  lamp  and  the  proper  spacing,  in  the  relation  of  these  two 
factors  to  the  success  or  failure  of  the  resulting  illumination, 
both  as  regards  directional  features  of  the  light  and  the  reduc- 
tion of  eye  fatigue,  is  such  as  to  make  these  two  items  of  the 
utmost  importance.  Therefore,  the  efficiency  of  a  system  should 
be  used  as  a  check  on  the  total  number  of  lamps  only  after  the 
size  of  the  lamps  and  their  spacing  have  previously  and  carefully 
been  determined.  Table  IV  shows  a  number  of  efficiency 
values  obtained  for  tungsten  lamps  under  actual  factory  condi- 
tions. It  must  be  remembered  that  these  values  are  modified 
by  the  condition  of  ceiling  and  wall  reflection,  together  with 
the  effect  of  dirt  and  dust  on  the  reflectors  or  globes. 

TABLE  IV. — AVERAGE  EFFICIENCY  VALUES  OF  TUNGSTEN  LIGHTING 
SYSTEMS  TESTED  UNDER  THE  SUPERVISION  OF  THE  AUTHOR* 

Average 
efficiency 
of  system 

Low  office 27 . 1  per  cent. 

Fairly  high  factory  office 27 . 4  per  cent. 

Low  factory  space 27      per  cent. 

Medium  high  factory  space 30 . 8  per  cent. 

Fairly  high  factory  space 29. 1  per  cent. 

All  efficiency  values  corrected  for  normal  lamp  voltage. 

"These  tests  were  taken  throughout  the  time  between  cleaning  intervals,  and  are  therefore 
averages  of  illumination  intensity  values  found  under  the  systems  when  both  clean  and 
soiled. 

17.  Point  Addition  of  Intensity  Values. — By  the  term  point 
addition  for  a  distributed  system  of  lamps  is  meant  the  calcula- 
tion of  the  intensity  of  light  at  a  given  point  on  the  working 

1  The  foot-candle  is  the  unit  of  illumination  intensity,  and  may  be  defined 
as  the  illumination  produced  at  a  point  one  foot  distant  from  a  source  of  one 
candle-power.  The  foot-candle  intensity  on  a  surface  multiplied  by  the. 
area  of  the  surface  in  square  feet  gives  a  product  which  is  called  lumens  of 
light  flux. 
2 


18  FACTORY  LIGHTING 

surface  produced  by  all  the  lamps  which  are  effective  in  illumi- 
nating that  point.  This  may  be  done  by  the  aid  of-  the  distribu- 
tion curve  of  the  lamps  in  question.  Fig.  5  shows  a  simple 
diagram  which  may  be  used  in  making  this  calculation.  It 
will  be  seen  from  this  diagram  that  the  candle-power  in  certain 
directions  is  divided  by  the  square  of  the  distance  between  the 
lamp  and  the  point  at  which  it  is  desired  to  add  together  the 
light  from  the  various  lamps,  the  result  being  the  intensity  in 
foot-candles  at  the  point  but  in  a  direction  parallel  to  the  ray  of 


.P.=  Candle  Power 
Direction  of  P 


.. 

F  Reference  Planet  v      in  Di 

------------  }»  ------  Ap 
I  <        Distance  from  Point  Directly  >  | 

below  Lamp  to  Point  P  K    Vertically  Downward 

Height  of          [  ^Intensity  at  Point  P 

Reference  Plane  \  j  r  p 

V  _  T        =      ~V     Cos  3  A 


Floor 

FIG.  5.  —  Diagram  for  illumination  calculations. 

light  from  the  lamp.  This  intensity  of  illumination  is  then  cor- 
rected so  as  to  secure  the  component  of  the  resultant  illumi- 
nation in  a  direction  perpendicular  to  the  working  surface.  It 
is  evident  that  this  calculation  must  be  made  for  each  lamp 
and  for  each  different  direction  in  which  the  light  rays  from 
the  various  lamps  strike  the  point  under  consideration.  It  is 
therefore  a  problem  of  some  length  to  calculate  the  illumination 
at  a  given  point  on  the  floor  space  in  those  cases  where  a  consid- 
erable number  of  lamps  is  used  to  illuminate  the  point. 

A  simple  method  has  been  devised,  however,  which  enables 
this  calculation  to  be  made  conveniently  by  the  use  of  a  rule, 
as  shown  in  Fig.  6.  In  Fig.  7,  for  example,  a  diagram  shows  the 


ILLUMINATION  DESIGN 


19 


location  of  the  lamps  on  a  given  floor  space  to  scale.  It  is 
assumed  that  the  lamps  are  mounted  10  ft.  above  the  surface 
of  the  work.  If  it  is  desired  to  calculate  the 
total  intensity  of  the  illumination  at  the  point 
"  A"  produced  by  all  the  lamps  which  contribute 
light  to  that  point  it  is  only  necessary  to  pre- 
pare a  simple  card-board  rule,  as  shown  in  Fig. 
6,  on  which  the  intensities  of  illumination  on  a 
plane  10  ft.  below  the  lamp  at  different  dis- 
tances from  a  point  perpendicularly  beneath  the 
lamp  are  indicated.  The  markings  on  this  rule 
are  made  to  the  same  scale  as  the  drawing,  while 
the  values  on  the  rule  are  calculated  by  the 
method  indicated  by  Fig.  5. 

It  is  convenient  to  place  this  rule  on  the  draw- 
ing as  shown  in  Fig.  7,  the  illumination  at  the 
point  "A"  due  to  each  lamp  being  read  directly 
from  the  rule.  Turn  the  rule  about  the  point 
"A"  until  it  intercepts  another  lamp,  and  the 
resultant  illumination  can  be  read  from  the  rule. 
After  proceeding  with  this  method  until  all  the 
lamps  have  been  intercepted  and  their  values  ob- 
served, the  values  as  a  whole  for  the  point  "A" 
are  added  together  numerically,  giving  the  re- 
sulting vertical  illumination  at  the  point  "A." 
The  term  vertical  as  here  used  refers  to  the  ver- 
tically downward  component  of  the  illumination 
produced  by  each  lamp  which  contributes  to  the 
intensity  at  the  point  "  A"  on  the  working  plane. 

By  this  means  the  intensities  at  a  sufficient 
number  of  points  on  the  working  plane  may  be 
determined  in  a  short  time  to  indicate  the  ap- 
proximate intensity  of  the  illumination  due  to 
certain  spacing  distances,  mounting  heights, 
types  and  sizes  of  lamps.  This  will  further  in- 
dicate whether  the  illumination  will  probably  be 
uniform  over  the  working  surface. 

The  point  addition  method  has  been  suggested 
as  a  means  for  calculating  the  arrangement  of 
lamps  for  new  lighting  systems.     Thus,  the  lamps  are  located  on 
the  floor  plan  outline  drawing  in  a  more  or  less  arbitrary  manner 


„    m 

1 

+3 

-a 

>t  Candlei 

Directly  1 

'1 
I 

Ip 

5 

^j 

a 

fl 

3 

.S 

l 

0 

•"  -^ 

£ 

Intensi 

stance  f  roi 

0 

'So 

™ 

Q 

<3 

JH 

-60'0 

S 

3 

O 

<D 

-SI'O 

S 

0 

-9ro 

3 

1 

a 

-OS'O 

- 

1 

-23'0 

a 

"o 

OH 

-SS'O 

3 

J? 

d 

-Ore 

OJ 

03 

-6TO 

oo 

SH 

-SS'O 

c- 

i 

c 

-02TO 

<s> 

d 

-^° 

* 

ag 

-w-o 

** 

f 

-H)'I 

CO 

i_ 

-II  'I 

CI 

1 

-LI'T 

- 

—  —  — 

0 
—  —  - 

20 


FACTORY  LIGHTING 


and  the  illumination  at  the  various  points  over  the  floor  space 
calculated.  If  the  intensity  is  not  sufficient,  another  arrange- 
ment is  given  trial  on  the  drawing,  and  the  lamps  either  shifted 
back  and  forth,  or  changed  in  number  or  size  until  the  intensity 
seems  to  be  sufficient  on  the  working  surface.  This,  however,  is 
open  to  the  objection  that  it  eliminates  the  question  of  size  of 
lamp  and  the  spacing  as  distinct  considerations.  These  two  items 
are  in  a  manner  quite  separate  from  the  uniformity  or  intensity 
of  the  light,  particularly  as  regards  the  directional  qualities  of  the 
illumination  effective  on  the  work.  Therefore,  the  method  of 


«         K 

K         K 

«         & 

•    «         K    !     K         K 

K          K     | 

0 

Reading?    U^ 

| 

«         K 

K         K 

H         H    « 

»  Jf 

^W         « 

«          «     | 

•    ®    o    8 

M    °    X    ' 

K   °  XA< 

'jr* 

«         K 

tt          «     | 

K         K 

Observa 
«            K 

ion  Points 
»            H 

H         « 

K         H 

K         H     | 

«         K 

K         K 

H            » 

«         K 

K         W 

«         «     | 

«         K 

K         H 

H            « 

K         « 

K         H 

W          K     | 

FIG.  7.  —  Diagram  to  illustrate  application  of  illumination  rule. 

point  addition  just  described,  as  well  as  the  method  of  efficiency 
as  described  in  Art.  16,  should  be  used  as  checks  only  after  the 
size  of  lamp  and  spacing  have  been  independently  determined. 
It  should  be  kept  in  mind  that  the  point  addition  method  of 
calculating  intensity  under  a  lighting  system  does  not  take  into 
account  reflection  from  walls  and  ceiling,  which  are  items  that 
may  materially  affect  the  results. 

18.  Problem  Illustrating  Steps  in  Typical  Design.— The  follow- 
ing case  is  given  in  detail  to  make  plain  the  various  steps  in 
working  out  a  typical  lighting  problem. 

Proposition. — Given  a  low  factory  space  with  ceiling  height 
of  12  ft.  6  in.,  and  columns  and  girders  so  arranged  that  the  bays 
have  dimensions  of  16  by  40  ft.  Clearance  between  crane  and 
ceiling  is  12  in.  and  the  ceiling  is  of  wood  with  a  very  dark 
surface.  There  are  no  walls  to  this  space,  as  it  is  simply  divided 


ILLUMINATION  DESIGN  21 

from  the  other  adjacent  shop  sections  by  columns.  The  work 
is  on  lathes,  together  with  some  assembly,  all  the  work  possessing 
very  dark  surfaces.  The  circuits  available  are  25-cycle  110-volt 
alternating  current. 

Required. — A  lighting  system  is  to  be  planned  which  will 
furnish  adequate  illumination  on  the  working  surface  approxi- 
mately 3  ft.  above  the  floor.  Individual  lamps  are  to  be  elimi- 
nated if  possible,  and  a  control  arrangement  of  the  lamps  provided 
which  is  flexible  enough  to  permit  of  turning  off  the  lamps  where 
not  required.  The  total  number  of  lamps  for  twenty  bays  are 
to  be  specified  as  well  as  their  spacing  and  mounting  height. 

Type  and  Size  of  Lamp. — Referring  to  Table  II  it  will  be 
found  that  for  a  12-ft.  ceiling,  lamps  of  approximately  80  candle- 
power  are  used  in  well  designed  systems.  The  surroundings 
being  dark,  a  unit  which  transmits  some  of  the  light  to  the 
ceiling  and  in  horizontal  directions  seems  advisable  on  account 
of  the  added  cheerfulness  thus  given  the  factory  space.1 

Owing  to  the  circuits  available  as  well  as  to  the  ceiling  height 
we  conclude  from  Table  I,  and  from  a  knowledge  of  the  candle- 
power  ranges  of  the  various  available  lamps,  that  the  tungsten 
type  seems  most  desirable.  This  conclusion  is  emphasized  by 
the  very  small  clearance  between  the  crane  and  ceiling,  which 
will  accommodate  a  tungsten  lamp,  but  not  an  arc  lamp.  The 
100-watt  tungsten  lamp  has  a  candle-power  of  80  and  is  therefore 
chosen. 

Spacing  the  Lamps. — A  diagram  of  one  of  the  bays  of  this 
location  16  by  40  ft.  should  now  be  drawn  and  the  lamps  located 
tentatively  to  scale  as  shown  in  Fig.  8,  according  to  Table  III. 
From  this  table  we  note  that  an  average  spacing  distance  for  a 
12-ft.  ceiling  ranges  from  8  to  10  ft.  Hence  in  a  direction 
parallel  to  the  length  of  the  aisle  an  8-ft.  spacing  of  lamp  rows 
conforms  to  the  table,  and  at  the  same  time  makes  the  lamps  sym- 
metrical with  respect  to  the  cross  girders,  while  a  10-ft.  spacing 
across  the  aisle  makes  the  lamps  symmetrical  to  the  width. 

1  This  statement  seems  to  violate  the  idea  that  all  of  the  light  should  be 
transmitted  in  useful  downward  directions  to  secure  the  highest  efficiency, 
because  obviously  the  light  transmitted  upward  in  a  proposed  system  like 
the  one  under  discussion  will  be  mostly  absorbed  by  the  dark  ceiling.  In 
gloomy  factory  spaces,  however,  it  may  be  an  advantage  to  sacrifice  some- 
what in  efficiency,  if,  by  using  glass  reflectors  which  transmit  some  of  the 
light  in  upward  and  horizontal  directions,  the  location  is  rendered  more 
pleasing  in  appearance. 


22 


FACTORY  LIGHTING 


These  spacing  distances,  conforming  to  the  averages  from  Table 
III  and  giving  a  symmetrical  arrangement,  are  chosen. 

We  should  now  check  the  chosen  size  and  the  spacing  dis- 
tances which  have  been  determined  separately,  in  order  to  ascer- 
tain if  the  resulting  illumination  will  probably  be  uniferm  over 
the  floor  area,  and  of  sufficient  intensity.  The  spacing  of  8 
by  10  ft.  results  in  one  100-watt  tungsten  lamp  for  each  80 


FIG.  8.- 


Elevation 
-Diagram  of  typical  factory  bay  showing  lamp  locations. 


sq.  ft.  In  Art.  16,  under  the  subject  of  lighting  system  efficiency, 
we  find  in  Table  IV  efficiency  values  of  about  30  per  cent,  through- 
out the  interval  between  cleanings  for  factory  conditions. 
The  100-watt  lamps  in  say  two  bays  furnish  16  X  830,  or  about 
13,280  lumens  of  light  flux.1  With  an  efficiency  of  30  per 

1  There  are  16  lamps  in  two  bays  and  each  lamp  furnishes  about  830  lumens 
at  a  given  rating.  Two  bays  are  taken  merely  to  give  an  average  effect,  as 
the  illumination  at  any  point  on  the  floor  is  made  up  of  the  light  received 
from  all  the  lamps  moderately  near  the  point,  and  also  because  in  some 
systems  the  edge  lamps  are  not  one-half  the  spacing  distance  between 
lamps,  from  the  walls. 


ILLUMINATION  DESIGN  23 

cent.,  the  total  number  of  lumens  on  the  1,280  sq.  ft.  lighted 
by  the  16  lamps  would  approximate  4,000,  that  is  30  per  cent, 
of  13,280.  Dividing  the  available  lumens  on  the  working 
surface  by  the  area  over  which  they  are  distributed  we  have 
4,000  divided  by  1,280  or  3.1  foot-candles  as  the  intensity  on  the 
working  surface.  Table  V  shows  this  to  be  adequate  for  factory 
work  of  the  kind  described.  It  must  be  remembered  that  the 
intensity*  as  just  calculated  is  an  average  between  cleanings 
of  lamps  and  reflectors,  and  its  value  will  therefore  be  less 
than  calculated  values  based  on  clean  lamps  and  reflectors. 

TABLE.  V. — ILLUMINATION  INTENSITIES  RECOMMENDED  FBOM  THE  EXPE- 
RIENCE OF  THE  AUTHOR  FOR  CERTAIN  CONDITIONS 

This  table  is  suggestive  only,  as  fixed  rules  may  mislead 


Class  of  work 

Foot-candle  intensity 

Office                                          

3.0 

Drafting 

7  0 

Factory  storage          

0.5 

Factory  rough  manufacturing  work 

3  0 

Factory,  fine  manufacturing  work  

5.0 

Power-house  .  . 

3.5 

Note. — These  values  indicate  good  working  intensities.  While  consider- 
ably higher  than  found  in  a  large  number  of  existing  lighting  systems,  they 
are  reasonable  for  each  class  of  work  involved,  always  assuming  that  engin- 
eering judgment  will  be  used  in  applying  such  information. 

Mounting  Height. — The  clearance  between  crane  and  ceiling 
determines  in  this  case  the  mounting  height,  which  is  approxi- 
mately 12  ft.  The  average  spacing  being  9  ft.,  we  divide  this 
by  9,  the  mounting  height  above  the  machines,  and  find  the  ratio 
between  spacing  and  mounting  to  be  1,  which  according  to  Art. 
9,  footnote,  is  nearest  to  the  intensive  type  of  reflector.  For  the 
conditions,  this  arrangement  should  provide  practically  uniform 
illumination  over  the  working  surface.1 

Point  Addition. — Making  a  diagrammatic  sketch  of  six  bays 
as  shown  in  Fig.  9,  drawn  to  a  scale  of  1/8  in.  to  the  foot,  and  by 
the  use  of  an  illumination  rule  as  shown  in  Figs.  6  and  7,  adapted 
to  an  intensive  type  reflector  for  the  height  in  question,  the  illu- 

1  The  calculations  up  to  this  point  are  usually  sufficient  to  give  a  general 
idea  of  the  lay-out  of  a  proposed  system,  and  especially  so  where  rules 
governing  the  ratio  of  spacing  to  mounting  are  available.  Often,  however, 
it  is  necessary  to  check  the  preliminary  lay-out  as  to  uniformity  and  intensity 
as  in  the  case  of  arc  lamps  or  other  types  with  which  such  ratio  constants  may 
not  be  furnished,  and  the  subsequent  paragraphs  on  point  addition  then 
become  important. 


24 


FACTORY  LIGHTING 


mination  may  now  be  integrated  at  each  of  several  points  as 
furnished  by  all  the  lamps  contributing  light  to  each  point,  in 
order  to  check  the  value  of  the  resulting  illumination  from  the 
method  worked  out  under  the  efficiency  scheme. 

Taking  the  point  "A"  and  placing  the  end  of  the  rule  at  this 
point,  the  illumination  at  the  point  "  A"  produced  by  lamp  (1)  is 
found  to  be  0.20  foot-candle;  that  produced  by  lamp  (2)  at  the 
point  "  A"  is  0.95  foot-candle;  by  lamp  (3)  is  0.95  foot-candle;  by 
lamp  (4)  is  0.20;  by  lamp  (5)  0.20;  by  lamp  (6)  0.95;  by  lamp 


NM-i-s'-h*4- 

H      «  \-ffi  V. 

1       1  -' 

H     H 

H     H 

H     H 

f 

H     H 

-Hj-  Hi 

H     H 

? 

Ao     oH 

H     H 

He    H? 

H"  H 

H     H 

K     H 

H     H 

*H 

H     H 

H     H 

H     H 

H     H 

Plan 

FIG.  9. — Diagram  of  six  factory  bays  with  points  for  illumination  rule 

addition. 

(7)  0.95;  and  by  lamp  (8)  0.20  foot-candle.  Hence  the  total 
illumination  intensity  at  the  point  "A"  produced  by  the  eight 
lamps  which  mainly  affect  this  point,  is  about  4.60  foot-candles. 
In  like  manner  it  is  found  that  the  illumination  at  the  point 
"B"  is  4.84  foot-candles;  at  point  "C"  4.60;  at  point  "D" 
4.34;  at  point  "E"  3.93;  at  point  "F"  4.94;  at  point  "G"  4.52; 
and  at  point  "H"  4.94  foot-candles.  Hence  the  average  inten- 
sity which  may  be  expected  over  this  factory  bay  based  on  the 
eight  points,  and  with  clean  lamps  operated  at  normal  voltage 
is  about  4.6  foot-candles.1  Allowing  say  30  per  cent,  for  deteri- 
oration between  cleanings  due  to  accumulations  of  dust  and  dirt 
on  reflectors  and  lamps,  this  results  in  a  minimum  of  say  3.0 

1  These  values  indicate  that  the  illumination  should  be  fairly  uniform  on 
a  plane  say  3  ft.  above  the  floor,  but  since  the  calculations  are  often  based 
on  an  uncertain  distribution  curve  of  the  reflector  and  do  not  take  into 
account  the  effect  of  surroundings,  they  should  not  be  relied  upon  further 
than  as  a  guide  to  the  probable  uniformity  of  the  resulting  illumination, 
unless  the  distribution  curve  of  the  reflector  is  reliable  and  surroundings 
be  given  due  weight  in  the  conclusions. 


ILLUMINATION  DESIGN 


25 


foot-candles,  and  hence  checks  in  a  close  manner  with  the 
intensity  thought  available  from  the  efficiency  method,  further 
verifying  the  conclusions  as  to  size  of  lamp  and  the  spacing. 

Switch  Control  and  Number  of  Lamps. — A  flexible  and  practical 
method  of  controlling  the  lamps  in  each  bay  is  shown  in  Fig.  8, 
the  lamps  controlled  from  each  switch  being  indicated  by  the 
same  numeral.  According  to  the  calculations  as  just  described, 
eight  lamps  are  required  in  each  bay,  making  a  total  of  160 
lamps  for  the  20  bays  to  be  lighted. 


FIG.  10. — Reproduced  from  a  photograph  taken  at  night  under  the  arti- 
ficial light  in  the  factory  space  discussed. 

The  Actual  Results  of  this  Installation  as  Made. — It  is  of 
interest  to  note  that  the  location  corresponding  to  this  example 
was  equipped  with  100- watt  tungsten  lamps  mounted  11  ft.  6  in. 
above  the  floor,  with  a  spacing  of  8  by  10  ft.  as  shown  in  Fig.  9 
and  in  Fig.  10.  The  intensity,  as  recorded  from  test  measure- 
ments, was  about  3.1  foot-candles  with  fairly  clean  lamps  and 
reflectors,  and  the  efficiency  about  30  per  cent.  The  actual 
conditions  thus  found  are  somewhat  lower  than  might  have  been 
expected  from  the  point  addition  calculations,  probably  because 
the  lamps  were  operated  a  trifle  below  their  normal  voltage  at 
the  time  of  making  the  test,  or  the  distribution  curve  of  the 


suauirq  duii3[  j^o^  A"q  paptA 
-ip  Qutsid  aupjJOM  no  euara 
-nq;  •uia^sA's  jo  Xouaionjg 


MUM  jad  suaumrj 


sajpueo-^ooj  m  A^ISUS^UJ 


3{JOAV 


joog 


iiii 


lili.il  .  .. 

•3     M3JSS  .-3   .as: 

•+3  -^  •£  c3  +=  •£  J2  o3  on*  c3  e3 

liSS  *£  rf  13^** 

.^H  ^3  a-*3  ^*  ^  ^  ^  >  ^> -^  • 


. 

l  ||          "TiTfTT 


Ml  M  b£> 


T       -o 
!3      * 


> 


^  ^ 

O5O5    .OT:OOOO     OOOOOOOao 

M  ' 

02      CO 


^        ^3  LL. 


rt<       COlOOOCCKNiM 


rH       CD  O5  CO 


<NCOCO(NCO(NCO<N       COCv|CO'-HC<icO       CO(M<NIM(N(N(Mr-i 


05  CD  •*  (M  »O  t>  CO  (N       NO5'*»C'C«5       IN  CO  rH  CD  <N  00  00  b- 
CO  CO  Tf*  CO  Tt<  CO  Tfl  l>       M<  (N  »C  CO  Tt<  CO       CO  Tj*  CO  <£!  CO  CO  CO  (N 


a  d  d  d  d  odd      d  d  d  d  d  d      d  d  d  d  d  d  d  d 


O  Tt<  rH  -tf  CO  O5  rH  CO          CO  O5  rH  l^  O  CO          O  OS  O  CO  O  O  O  O 

^  t^  CO  t^  t^  CO  CO  Oi   t^iCt^-iCOSt^   00  00  O  00  00  00  00  1C 


,£!  XJ  rD  rQ -O -Q -Q  rD 

dddddddd 


OOOOOOOC 


1C  t^  CO  *C  1C  1C  CO  00       COiCiCiCOOt^       00  00  00  00  00  00  00  <M 


D.  a  a 

OOO 


OOOOOOOA  o 


-+^>   +3   +3  —     —     — 

03  03  o3        c3  o3  03 

=  =  =    s  s  s 

.2.2.2  0.2.2.2 


sssss 

2  ro  ^  ^  °° 
'C'E'C'E'C 


assa 


aa 


III  2 j||l  -sggggg  «g 


a  a  a  a     a 

03^3  c3 


. 
OOOOOO  OOOOOOOO 

__  ______^__ 


'S5S 


§0000000     oooooo     oooooooo 
CO  CO  CO  CO  CD  CO  CO        CO  CO  CO  CO  "C  CO        CDOO>COOO»C 


ddddd    dddddd   dddddddd 


NCO^H       OCOO505OO       COOOOOOOCO 


O5OOOOO>-iCl       OOOOOCO-<*iO       t^  i-l  (N  O>  CO  CO  CO  1-1 


OOOOOOCOiC       00  O5  rH  CO  CO  CO       00  rH  (N  CO  CO  CO  CO 


26 


ILLUMINATION  DESIGN  27 

reflector  from  which  the  illumination  rule  was  made,  may  have 
indicated  candle-power  values  higher  than  the  actual. 

It  is  instructive  to  note  that  the  actual  illumination  produced 
where  the  surroundings  are  bright  may  be  appreciably  higher 
than  indicated  by  preliminary  point  addition  calculations, 
on  account  of  reflection  from  walls  and  ceilings.  Further,  the 
efficiency  of  a  system  may  be  appreciably  lower  than  the  pre- 
liminary efficiency  calculations  would  indicate,  if  the  surroundings 
are  darker  than  assumed,  and  vice  versa. 

Note. — From  what  has  been  set  forth  in  the  foregoing  discussion  it 
may  be  thought  that  illumination  calculations  are  not  only  complex  but 
without  system.  In  this  connection  it  should  be  clearly  stated  that  the 
object  of  the  discussion  on  illumination  design  has  been  to  describe  the 
practical  reasoning  which  should  be  followed  in  work  of  this  kind.  It 
has  not  been  the  intention  to  formulate  a  set  of  definite  rules,  but  rather 
to  get  away  from  the  idea  of  constants  and  formulae,  and  instead  to 
describe  the  methods  which  are  used  in  the  practical  planning  of  lighting 
systems.  As  illuminating  engineering  work  advances  and  accurate  data 
accumulates,  it  is  reasonable  to  suppose  that  the  design  of  lighting  sys- 
tems will  become  more  the  result  of  engineering  judgment  .than  is  now 
the  case.  Until  then,  such  work  should  be  conducted  in  the  careful  and 
painstaking  manner  described  in  the  preceding  paragraphs. 

In  numerous  cases  where  the  refinements  as  here  discussed  cannot, 
through  a  lack  of  working  knowledge  on  the  part  of  the  designer,  be  con- 
sidered, there  will  be  found  on  the  market  a  limited  number  of  groups 
of  reflectors  that  may  be  used  for  tungsten  lamps.  If,  therefore,  tungs- 
ten lamps  are  to  be  used,  the  determination  of  that  group  of  reflectors 
adapted  to  given  conditions  may  be  made  in  a  fairly  simple  manner, 
either  by  securing  this  information  from  the  reflector  companies,  or 
through  the  medium  of  published  information  relating  to  various 
reflectors.  The  illumination  resulting  from  the  selection  of  a  given  type 
of  reflector  for  a  given  type  of  lamp,  based  on  the  data  furnished  by  the 
reflector  manufacturers,  is  apt  to  produce  a  fairly  satisfactory  result, 
even  without  any  considerable  amount  of  calculation. 

Where  extensive  work  is  to  be  undertaken,  however,  it  is  very  desirable 
to  do  away  as  much  as  possible  with  rules  and  formulae  as  generalized 
information,  and  to  use  them,  if  at  all,  only  in  conjunction  with  the 
methods  herein  set  forth.  The  information  furnished  in  rule  books  or 
in  tables  such  as  Table  VI  will  then  be  merely  a  guide  to  an  intelligent 
application  of  engineering  methods. 

It  should  always  be  kept  in  mind,  however,  that  even  the  most  care- 
fully prepared  plans  for  lighting  may  produce  results  far  different  than 
anticipated  if  due  allowance  is  not  made  for  reflection  from  or  absorption 
by  walls,  ceilings,  and  surrounding  objects. 


CHAPTER  III 
LIGHTING  INSTALLATION  WORK 

19.  The  installation  of  a  lighting  system  includes  the  wiring 
and  the  placing  of  switches,  lamps  and  reflectors  according  to 
pre-arranged  plans. 

In  the  preceding  chapter  it  was  shown  that  illumination 
design  fundamentally  considers  the  proper  location  of  lighting 
units  to  secure  a  definite  and  advantageous  result.  It  is 
obvious  that  in  planning  new  lighting  systems  the  details  of 
the  building  construction  should  be  taken  into  account,  and 
that  lamps  should  preferably  not  be  placed  where  it  is  incon- 
venient to  mount  them. 

From  the  standpoint  of  the  designing  engineer,  the  wire- 
men  should  be  posted  in  this  work  concerning  the  importance 
of  accurately  locating  the  lamps  according  to  the  plan.  It 
will  thus  be  apparent  that  there  are  two  viewpoints,  the  one 
that  of  the  designer,  and  the  other  that  of  the  wiremen.  Hence 
the  need  for  a  co-operative  spirit  between  illuminating  engineers 
and  wiring  foremen  or  contractors,  without  which  such  work  is 
apt  to  be  less  successful  than  otherwise. 

20.  Theory  and  Practice. — The  illuminating  engineer  should 
consider  at  the  outset  the  object  of  adapting  certain  lamps  to 
specific  purposes,  and  should  determine  the  locations  for  these 
lamps  in  a  manner  to  produce  the  most   effective  result.     In 
following  this  plan  of  procedure,  however,  he  should  keep  in 
mind  that  slight  changes  in  lamp  locations  often  reduce  the  cost 
of  wiring  to  such  an  extent  that  the  differences  in  the  illumi- 
nation are  small  compared  to  the  greater  ease  in  mounting  the 
lamps  according  to  the  modified  plan. 

The  first  duty  of  the  designer,  however,  is  to  distribute  the 
outlets  for  the  lamps  in  such  a  way  that  the  illumination  shall 
be  satisfactory  for  the  conditions  in  question,  and  after  this 
determination  has  been  made,  an  inspection  should  follow  to 
ascertain  whether  or  not  certain  small  changes  may  be  an 
advantage  in  order  to  accommodate  wiring  conditions.  This  is 
a  factor  of  importance,  perhaps,  more  in  the  case  of  buildings 

28 


LIGHTING  INSTALLATION  WORK 


29 


already  constructed  than  where  the  wiring  is  to  be  installed 
during  the  process  of  construction. 

A  careful  balance  between  engineering  accuracy  and  the 
practical  application  of  the  plans,  is  apt  to  result  most  success- 
fully for  all  concerned. 


25K.W 

Service  Supply  x 


50  Circuit  Panel  Box1 
-Locate  2  Pole  Switch  here 


FIG.  11. — Wiring  plan  showing  conduit. 

21.  Installing  Lamps  According  to  a  Fixed  Plan. — The  work- 
ing plans,  to  be  most  easily  interpreted  by  the  wiring  foreman, 
should  define  all  items  of  information  necessary  to  permit  the 
installing  of  the  lamps  in  accordance  with  the  same. 

The  drawing,  as  explained  in  Art.  15,  should  indicate  the 
location  of  the  lamps  to  scale,  and  a  list  of  materials  should 


30 


FACTORY  LIGHTING 


either  be  placed  on  the  drawing  or  on  accompanying  specifications. 
Fig.  11  represents  a  wiring  arrangement  and  the  various  sizes  of 
conduit  together  with  panel  box,  transformer  and  the  control 
arrangement,  the  latter  by  means  of  dotted  lines  which  enclose 
the  lamps  controlled  from  a  single  switch. 

In  wiring  work  the  conditions  are  likely  to  be  trying,  and, 
especially  in  factories  where  production  must  not  be  delayed  by 
wiring  work,  it  is  necessary  in  as  far  as  possible  to  facilitate  the 
wiring  by  complete  information. 


Toggle  Bolt 


_^__      Metal  Moulding 
Conductors 
FIG.   12. — Toggle  bolt  used  for  holding  moulding  to  tile  ceilings. 

22.  Estimating  the  Cost  of  the  Work. — After  the  completion 
of  a  drawing,  it  is  advisable  to  make  an  estimate  of  the  expense 
connected  with  the  installation  of  the  system.  The  estimate 
is  comparatively  simple  if  the  drawing  contains  the  necessary 
circuits  and  control  features.  A  practical  form  is  shown  in 
Table  VII,  which  may  be  followed  approximately  in  estimating 
on  such  work. 

TABLE  VII. — SHOWING  ITEMS   INVOLVED  IN  A  TYPICAL  LIGHTING  ESTI- 
MATE.    THE  COSTS  ARE  TO  BE  ADDED  AFTER  EACH  ITEM  AND 
THE  TOTAL  THEN  INDICATES  THE  ENTIRE  ESTIMATED 
COST  OF  MAKING  THE  INSTALLATION 


Amt.  Item 

268  100-watt,  112-volt  clear  Tungs- 
ten lamps. 

268  Type  "1-9"    Holophane  reflect- 
ors. 

268  Form  "H"  holders. 
268  Keyless  sockets. 
268  Fused  rosettes. 
268  Wood  socket  bushings. 

67  10-amp.  snap  switches. 

17  Fuse  blocks. 

34  Fuse  plugs. 

34  Fuses. 


Amt.      .  Item 

134  ft.  No.  16  lamp  cord. 
40  Conduit  boxes. 
400  ft.  1/2  in.  Loricated  conduit. 
1500  ft.  2-wire  moulding  and  cap. 
2  gro.  1   1/4-in.  No.  8  F.  H, 

wood  screws. 
5000  ft.  No.  12  R.  C.  wire. 

4  rolls  Friction  tape. 

5  Ib.  Solder. 

Labor. 

Over-head  charges. 
Total. 


LIGHTING  INSTALLATION  WORK  31 

The  cost  per  outlet  is  of  particular  importance  and  may  be 
used  as  a  unit  of  comparison  between  the  cost  of  the  proposed 
system  and  that  of  other  systems  previously  installed,  to  deter- 
mine whether  or  not  the  plans  proposed  are  either  extravagant, 
on  account  of  certain  arrangements  which  may  be  modified,  or  as 
showing  the  wiremen  what  is  expected  of  them  in  the  economy  of 
making  the  installation,  a  valuable  item  where  the  work  is  under 
the  supervision  of  the  electrical  department  of  a  plant. 

"It  is  highly  desirable  in  large  plants  to  keep  a  record  of  all 
such  estimates  until  the  work  of  a  given  installation  is  complete, 
and  then  to  follow  up  the  original  estimate  by  checking 
the  actual  costs  with  the  same.  These  exact  costs  can  then  be 
filed  for  future  reference  when  additional  work  is  considered. 


FIG.  13. — Plain  wood  ceiling,  no  under  beams. 

23.  Relation  of  Ceiling  Construction  to  Wiring  Expense. — The 

nature  oi  the  ceiling  obviously  has  a  large  influence  on  the 
expense  of  installation.  Industrial  buildings  present  a  large  va- 
riety of  ceiling  construction,  some  of  which  may  be  indicated  as 
follows : 

(1)  Wood  ceilings  with  no  under  beams  or  joists. 

(2)  Wood  ceilings  with  under  beams  or  joists. 

(3)  Plaster  ceilings  or  concrete  construction. 


32 


FACTORY  LIGHTING 


(4)  Tile  ceilings  covered  with  plaster. 

(5)  Brick  ceilings  arched,  with  iron  girder  supports. 

(6)  Open-girder    construction    where   the    only   support   for 
the  lamps  and  wiring  is  either  on  the  trusses  or  on  stringer 
boards  located  between  the  same,  unless  the  .wiring  and  lamps 
are  attached  directly  to  the  roof  of  the  building  and  the  lamps 
suspended  in  such  a  way  as  to  avoid  shadows  which  result  on  the 
work  if  they  are  located  above  and  too  nearly  in  line  with  the 
iron  work. 


FIG.  14. — Wood  ceiling  with  under  beams. 

The  simplest  wiring  problems  are  associated  with  wood 
ceilings  in  those  buildings  where  the  lamps  are  to  be  installed 
after  the  construction  of  the  plant.  Here  the  wires  may  be 
attached  directly  by  means  of  porcelain  knobs  or  cleats,  by  ..wood 
moulding,  or  in  some  cases  conduit  may  be  attached  directly  to 
the  ceiling. 

Where  the  wood  ceiling  is  divided  into  sections  by  under 
beams  or  joists  it  is  usually  best  to  arrange  the  various  circuits 
to  be  self-contained  in  each  bay,  thus  avoiding  the  necessity  of 
extending  the  control  circuits  either  through  or  beneath  the 
beams. 

With  plaster  or  tile  ceilings,  the  problems  of  attaching  the 


LIGHTING  INSTALLATION  WORK 


33 


wires  in  old  buildings  is  complicated  by  the  finding  of  lodgment 
for  screws  or  bolts.  A  toggle  bolt  may  be  used  by  drilling  the 
tile,  forcing  the  toggle  bolt  into  place,  which  when  pulled  down 
is  anchored  on  the  inner  side  of  the  tile  as  shown  in  Fig.  12. 
Knobs,  cleats  or  any  of  the  various  types  of  moulding  may  then 
be  attached  to  these  toggle  bolts. 

To  arched  brick  ceilings  small  boards  may  be  attached  either 
directly  or  preferably  through  the  medium  of  drilling  the  iron 


FIG.  15. — Tile  ceiling  covered  with  plaster. 


work  at  the  bay  intersections.  The  wiring  may  conveniently  be 
mounted  on  these  boards. 

With  open-girder  construction  several  methods  maybe  adopted. 
One  scheme  is  to  attach  the  wires  to  the  roof  and  to  drop 
the  lamps  by  means  of  cord  or  supporting  wires  to  a  level  or 
directly  below  the  iron  work.  Another  scheme  is  to  attach 
stringer  boards  to  the  under  side  of  the  horizontal  iron  work  and 
to  support  wires  and  lamps  on  these  boards. 

The  foregoing  statements  apply  in  general  to  those  cases  where 
the  wiring  is  put  in  immediately  after  the  building  has  been 


34  FACTORY  LIGHTING 

constructed  or  in  old  buildings  as  open  work.     Some  of  the  types 
of  ceiling  described  are  shown  in  Figs.  13,  14,  15,  16,  and  17. 

24.  Following  up  the  Work.— After  turning  over  the  plans  to 
the  wiring  foreman,  it  is  an  advantage  to  the  engineer  in  charge 
to  visit  the  location  during  the  course  of  the  installation  in  order 
that  he  may  determine  the  accuracy  with  which  the  plans  are 
being  followed.  A  word  of  explanation  to  the  wiremen  now 
and  then,  before  the  work  is  well  under  way,  may  avoid  serious 
errors  in  the  location  of  lamps  through  a  possible  .misunder- 


FIG.  16. — Brick  ceiling  with  iron  girder  supports. 

standing  of  certain  items  on  the  drawing,  although  this  possibility 
is  reduced  where  the  plans  contain  full  information. 

In  some  cases  it  may  be  best  to  locate  the  lamps  as  originally 
planned,  irrespective  of  the  difficulty  or  expense.  Judgment, 
however,  should  be  exercised  in  this  connection  and  wherever  an 
obstacle  seems  to  be  serious  enough  to  warrant,  a  modification 
in  the  original  plans  should  be  made  to  accommodate  the 
difficulty. 

25.  Underwriters'  Rules. — All  wiring  should  be  installed  in  a 
correct  and  permanent  manner,  not  only  to  insure  reliable  service 


LIGHTING  INSTALLATION  WORK  35 

but  also  to  adhere  to  the  Rules  of  the  National  Board  of  Fire 
Underwriters. 

26.  Supporting  the  Lamps  Securely. — In  view  of  the  tendency 
to  use  a  large  number  of  lamps  for  given  areas,  positively  secure 
fittings  should  always  be  employed.  In  some  cases  there  is  no 
direct  means  of  support  above  the  location  of  the  lamp  and  in 
some  of  these  cases  special  stretched  wire  supports  have  been 
used  for  high  mounting  as  shown  in  Fig.  18.  The  lamps  are  run 
out  on  the  wires  from  a  point  at  the  center  of  the  aisle  to  a  posi- 
tion toward  the  side  of  the  building  and  here  it  is  of  the  utmost 
importance  to  anchor  the  ends  of  such  supports  securely. 


FIG.  17. — Open  girder  construction. 

Simple  brackets  may  be  used  in  some  instances  where  a  vertical 
roof  support  serves  also  to  support  the  lamp  in  order  to  bring 
the  lower  portion  of  the  lamp  on  a  level  with  the  over-head* 
horizontal  iron  work.  This  is  shown  in  Fig.  19. 

Large  tungsten  lamps  which  have  a  flexible  cord  connection 
between  the  rosette  at  the  ceiling  and  the  socket  should  be  rein- 
forced by  means  of  small  chains  which  may  be  attached  to  the 
shade  holder  on  the  one  hand  and  to  the  ceiling  on  the  other,  as 
shown  in  Fig.  20. 


36 


FACTORY  LIGHTING 


Glass  globes  and  reflectors  should  be  enclosed  with  a  fine- 
mesh  screen  to  prevent  accidental  falling  of  the  reflector  in  case 
it  becomes  detached  from  the  holder,  or  if  broken,  to  prevent 
small  pieces  of  glass  from  falling.  Such  a  mesh  screen  is  shown 
for  an  arc  lamp  globe  in  Fig.  21,  and  for  a  glass  reflector  in 
Fig.  22. 

The  foregoing  items  are  of  much  importance  on  account  of 
the  danger  to  employes  when  constantly  moving  under  large 
numbers  of  over-head  lamps  as  suggested  by  Fig.  23.  Some 
reflectors  are  very  heavy  and  the  danger  should  they  become 


FIG.  18. — Stretched-wire  supports  for  arc  lamps. 

•  % 

detached  through  the  result  of  insecure  fittings  is  apparent. 
With  glass  reflectors  the  holder  by  which  the  reflector  is 
attached  to  the  socket  should  be  securely  fastened.  The  so- 
called  spring  type  holder  has  been  used  to  great  advantage,  and 
the  flexibility  of  its  fitting  is  such  as  to  make  it  particularly 
well  adapted  to  glass  reflectors  for  tungsten  lamps. 

27.  Control  Circuits. — Wall  switches  should  be  placed  on 
similar  portions  of  the  wall  or  on  relatively  the  same  column 
locations  throughout  the  building,  that  is,  on  the  same  side  of 
each  column  and  on  the  same  side  of  the  aisle.  This  will  avoid 
confusion  when  lamps  are  turned  on  or  off  in  large  numbers  a 
few  at  a  time. 


LIGHTING  INSTALLATION  WORK 


37 


•  Such  control  circuits  are  largely  run  from  the  lamps  to  a  point 
within  reach  of  the  floor,  the  wires  being  run  down  either  the 
walls  or  the  columns.  The  expense  of  these  circuits  will  depend 
to  a  great  extent  on  the  ease  or  difficulty  with  which  the  wires 
can  be  attached  to  walls  or  columns,  and  also  on  the  distance 
between  the  switch  and  the  lamps  it  is  to  control. 

In  many  cases  the  extension  of  elaborate  control  circuits  may 
almost  entirely  be  eliminated  by  the  use  of  the  pendant  or  pull 
switch.  By  this  means  the  circuits  are  controlled  through  the 
medium  of  switch  connections  at  the  ceiling  directly  in  line  with 


FIG.  19. — Bracket  for  supporting  arc  lamps. 

the  wires  which  feed  each  circuit.  In  ordinary  factory  sections 
there  is  a  slight  disadvantage  connected  with  the  use  of  pendant 
switches.  They  are  often  hung  in  such  a  way  that  workmen 
walking  up  and  down  the  aisles  may  thoughtlessly  strike  or 
tamper  with  the  switch,  thus  causing  excessive  maintenance  and 
a  continual  annoyance  from  having  the  control  apparatus  out  of 
order.  The  use  of  the  pull  switch  practically  eliminates  this 
difficulty  in  that  it  makes  possible  the  mounting  of  the  switch 
itself  at  the  ceiling,  and  the  control  is  effected  by  a  cord  and  a 
small  handle  attached  to  the  same.  This  class  of  switch  is 
particularly  adapted  to  fairly  low  ceilings  and  also  where  com- 


38 


FACTORY  LIGHTING 


paratively  large  numbers  of  small  or  medium  sized  lamps  are 
used  with  a  relatively  large  number  of  switches. 

Where  the  factory  sections  are  fairly  wide  and  where  windows 
are  located  at  one  side  of  the  aisle  only,  the  floor  space  at  the 
center  of  the  building  in  the  early  morning  and  the  late  afternoon 
hours  may  be  practically  without  natural  light  in  comparison 
with  the  floor  space  near  the  windows.  As  stated  in  Art.  14,  if 
all  the  lamps  across  the  floor  are  controlled  from  one  switch  in 


Ceiling 


Chain  attached  to 
Shade  Holder  and 
Anchored  to  Ceiling 


FlG.   20.- 


-Small  chains  for  supporting  glass  reflectors  used  with  tungsten 
lamps. 


rows,  the  floor  space  at  the  center  of  building  will  often  be 
supplied  with  artificial  light  when  the  workmen  immediately 
adjoining  the  windows  will  still  be  supplied  with  adequate  natural 
light.  Hence  the  lamps  near  the  windows  should  be  on  a 
separate  circuit  from  the  'lamps  near  the  central  portion  of  the 
aisles.  This  is  indicated  in  Figs.  4  and  24  which  show  the  lamps 
controlled  in  rows  parallel  to  windows.  While  somewhat  more 
expensive  as  to  first  cost  than  where  a  large  number  of  lamps  is 
controlled  from  one  switch,  this  method  is  usually  an  economy 
in  the  long  run  due  to  the  flexible  control  arrangement.  Thus, 
lamps  not  required  near  the  windows  may  be  turned  out  without 


LIGHTING  INSTALLATION  WORK  39 

interfering  with  the  illumination  at  the  more  central  portions  of 
the  building. 

28.  Series  and  Multiple  Systems. — The  series  system  of 
lighting,  which  is  so  well  adapted  to  exterior  service  on  account 
of  its  simplicity  and  comparatively  low  cost  for  wiring  installa- 
tion, is  very  poorly  adapted  either  as  a  constant  current  or  a 
constant  voltage  system  for  interior  industrial  purposes.  The 
disadvantages  of  the  series  system  for  interior  work  are,  first,  the 
large  number  of  lamps  controlled  from  a  single  switch,  which 
implies  that  a  large  floor  area  is  apt  to  be  lighted  by  one  circuit 
of  lamps.  It  is  not  always  convenient  nor  economical  to  use 
all  the  lamps  on  a  single  series  circuit  at  one  time.  A  multiple 


FIG.  21. — Mesh  screen  used  with  arc-lamp  globes  to  prevent  falling  of  glass 
in  case  of  breakage. 

arrangement  of  lamps  where  each  lamp  or  small  group  of  lamps 
may  be  controlled  from  one  switch  permits  a  disposition  of  the 
circuits  to  far  greater  advantage  than  in  the  case'  of  series 
systems. 

A  second  disadvantage  of  the  series  system  is  the  high  voltage « 
usually  associated  with  its  use.  This  entails  a  greater  risk  to 
the  wiremen  when  working  on  such  circuits,  and  largely  on  ac- 
count of  this  risk  the  series  system  is  not  recommended  for 
interior  work.  In  those  instances  where  series  circuits  are 
already  in  use,  or  where  they  have  been  made  necessary  by 
other  special  circumstances,  care  should  be  taken  to  provide  a 
switch  at  each  end  of  the  circuit  and  these  switches  should 
both  be  open  when  wiremen  are  at  work  on  the  circuits. 


40  FACTORY  LIGHTING 

29.  Supply  Circuits. — With  the  prevailing  tendency  toward 
large  increases  in  the  illumination  in  factory  buildings,  the  in- 
stallation of  new  in  place  of  older  systems  calls  for  special 
attention  to  the  supply  circuits  on  account  of  the  large  amount 
of  energy  usually  required  even  with  higher  efficiency  lamps 
when  a  more  liberal  number  of  lamps  is  substituted  for  what  has 
previously  been  inadequate  illumination.  There  is  a  tendency 
to  make  use  of  old  circuits  for  supplying  new  arrangements  of 
lamps,  but  this  should  be  done  only  after  a  study  has  been 
made  of  the  new  power  requirements,  and  after  it  has  been 
determined  that  the  old  circuits  are  adequate  in  capacity  for  the 
new  conditions. 


FIG.  22. — Mesh  screen  used  with  glass  reflectors  for  tungsten  lamps  to 
prevent  falling  in  case  of  breakage. 

Electric  lamps  in  factory  work  should  always  be  supplied 
from  circuits  of  constant  voltage  to  secure  the  advantages  of 
steady  light,  and  also  from  the  standpoint  of  irriproved  operating 
conditions  where  the  voltage  is  uniform  in  value.  When  new 
circuits  are  provided,  the  mains  should  be  made  sufficiently  large 
to  permit  of  extensions  as  new  buildings  or  new  additions  are 
made  to  the  equipment. 

Power  and  lighting  circuits  should  be  separate,  on  account 
of  varying  demands  placed  on  combined  circuits  by  motor  loads. 
There  is  a  tendency  to  tap  in  a  motor  circuit  here  and  there 
on  lighting  mains  where  they  are  conveniently  located  with 
respect  to  the  machines,  but  a  rigid  adherence  to  the  separation 
of  motor  and  lighting  mains  is  best. 


LIGHTING  INSTALLATION  WORK  41 

An  accurate  diagram  or  map  of  the  wiring  in  the  factory 
should  be  on  file  so  that  changes  or  modifications  in  the  wiring 
may  be  made  without  the  necessity  of  tracing  out  the  mains  and 
circuits  on  the  floor.  The  difficulty  connected  with  obtaining 
such  a  wiring  map  in  an  old  plant,  as  well  as  the  work  of  keeping 
it  up  to  date,  is  small  in  comparison  to  the  convenience  it  affords 
for  wiring  changes,  while  in  a  new  plant  it  is  a  simple  matter  to 
secure  such  a  map  when  the  lighting  equipment  is  installed. 
Fig.  25  indicates  a  wiring  map  of  an  actual  installation  in  part 
and  from  this  an  idea  may  be  gained  as  to  one  method  of  re- 
ducing the  wiring  conditions  to  an  exact  diagram. 

30.  Methods  of  Installation  in  Relation  to  Maintenance.— The 
maintenance  cost  of  lighting  systems  is  largely  influenced  by  the 
accessibility  of  the  lamps.     With  moderate  ceiling  heights  up  to 
14  or  16  ft.  the  lamps  may  be  reached  from  a  step  ladder.     For 
ceiling  heights. above  16  ft.  it  is  hardly  practical  to  use  a  step 
ladder  and  where  it  is  impossible  to  reach  the  lamps  from  the  top 
of  a  crane,  it  is  sometimes  necessary  to  mount  the  lamps  suffi- 
ciently below  the  ceiling  to  make  them  accessible  from  a  ladder 
on  the  floor. 

Where  the  lamps  are  maintained  from  the  top  of  a  crane  care 
must  be  exercised  to  avoid  accidents  to  the  lamp  or  repair  men 
through  carelessness  in  getting  on  or  off  the  crane,  or  through 
the  movement  of  the  crane  while  the  lamp  man  is  at  work.  A 
rigid  rule  should  be  enforced  that  in  no  case  shall  the  crane  be 
moved  while  a  man  is  at  work  on  the  same. 

In  some  instances  where  the  lamps  are  mounted  very  high, 
small  wood  walkways  have  been  provided  up^  and  down  the 
aisles  and  above  the  crane.  This  walkway  is  attached  directly 
to  the  roof  trusses  in  such  a  manner  that  the  lamps  may 
readily  be  renewed  or  trimmed.  While  the  first  cost  for  such 
a  walkway  may  not  seem  warranted,  such  an  addition  in  large 
factories  forms  a  ready  access  to  the  lamps  without  interfering 
with  the  crane  service  and  this  in  the  end  will  usually  save 
considerable  time  in  the  operation  of  the  shop. 

Automatic  cutouts  may  be  employed  where  it  is  possible  to 
lower  lamps  from  high  positions.  The  lamps  when  lowered  by 
this  means  are  disconnected  from  the  supply  circuits,  and,  besides 
facilitating  the  maintenance  work,  added  safety  is  thus  insured 
the  lamp  men. 

31.  Economy  in  Using  Wiring  Material. — In  turning  a  light- 


42 


FACTORY  LIGHTING 


ing  plan  over  to  the  wiring  foreman  where  no  indication  is  made 
as  to  the  amount  of  wiring  material  required,  undue  amounts  of 
material  may  be  wasted  in  cutting  wire  or  conduit  lengths,  with- 
out regard  to  the  limits  of  spacing  between  lamps.  For  this 
reason  it  may  be  desirable  to  show  the  fittings  and  dimensons  in 
such  a  way  that  the  lengths  of  wire  and  other  material  may  be 
made  up  in  an  accurate  manner.  In  large  installations  the  por- 
tions of  moulding  or  conduit  cut  off  the  ends  of  poorly  matched 
pieces  of  material  may  run  into  a  relatively  large  expense. 


FIG.  23. — Typical  factory  lighting  system  showing  the  large  number  of 
glass  reflectors  over  the  workmen.  These  reflectors  are  supported  by  small 
chains  to  the  ceiling  and  covered  with  wire  mesh  screens. 

32.  Tungsten  Lamps  Under  Shop  Conditions. — The  growing 
use  of  tungsten  lamps  for  moderate  ceiling  heights  in  many 
factory  buildings  has  in  the  past  been  somewhat  hindered  by  the 
objection  of  filament  breakage  from  vibration  of  the  lamps. 
Many  devices  have  been  suggested  for  reducing  the  shock  or 
vibration  under  rough  shop  conditions.  These  so-called  shock 
absorbers  are,  however,  unnecessary  in  general  if  a  small  piece 
of  flexible  cord  from  one  to  two  or  more  inches  long  is  connected 
between  the  rosette  at  the  ceiling  and  the  socket.  This  small 


LIGHTING  INSTALLATION  WORK 


43 


length  of  cord  is  sufficient  to  absorb  practically  all  shock. 
Furthermore,  the  recent  developments  of  the  drawn-wire  tungsten 
filaments  under  the  trade  name  of  Mazda  lamps,  have  greatly 
reduced  the  breakage  due  to  vibration,  so  that  at  the  present 
time  tungsten  lamps  are  used  very  generally  in  many  factory 
buildings  even  under  very  rough  service. 

Where,  however,  the  lamps  must  be  supported  among  line 
shafting  and  belting,  it  is  advisable  to  eliminate  flexible  cord  in 
mounting  the  lamps  on  account  of  the  danger  from  the  accidental 
flying  off  of  belts.  In  such  cases  the  lamps  may  be  mounted 
rigidly  to  the  ceiling  by  means  of  gas  pipe  or  conduit. 


r 

«6  «7  #7 


«6  #7  #7  «7 

«9  «10  «10  «10 

«9  «io  K«>  ft10 

^11   ^11  ^12  ^12  ;c(i2§ 

)^11      ^11  )^12  )^12  £ 


FIG.  24. — Control  of  lamps  parallel  to  windows.     (See  also  Fig.  4.) 

33.  Installing   Small  Numbers  of  Lamps  at   a  Time. — The 

necessity  for  a  revision  of  old  lighting  systems  sometimes  calls 
for  extensive  improvements.  In  such  cases  factory  managers  are 
apt  to  be  confronted  with  an  expense  which  they  may  not  be  able 
to  bear  at  any  one  time.  A  method  which  has  been  employed 
in  some  instances  is  to  draw  up  complete  plans  for  one  section 
of  the  factory  after  another,  and  to  extend  the  installation 
period  over  a  comparatively  long  time.  A  small  portion  of  the 
new  system  may  then  be  installed  one  month,  another  portion 
the  following  month,  and  so  on. 

In  such  cases  the  system  as  a  whole,  if  possible,  should  be 


44 


FACTORY  LIGHTING 


planned  before  beginning  the  work,  at  least  as  regards  given  de- 
partments of  the  factory,  so  that  the  final  arrangement  of  lamps 
may  conform  to  a  systematic  plan.  An  additional  advantage  of 
this  scheme,  especially  where  experiments  are  contemplated  for 
ascertaining  the  best  method  of  illumination  for  given  purposes, 
is  the  ability  it  gives,  after  the  installation  of  the  first  small 

Column  Numbers 


7         18 

®  a 

a  o> 

2C 

d 

0> 
^MoJ 

2 

1        22        2} 

g    1 
^£§.1 

5        24 

25        26        2J 

Aj 

29 

C?     |>» 

,      3( 

i 

)        8 

| 

iJ    &j 

S| 

II 

1  Hi 

II 

11 

a  3 

i  \       \  ^ 

1     ^  1 

2 

HJ 

Hh^ 

LH.J  1 

^ 

E-I  j 

rH       1 

IfH        1 

o 

Q 

0       I 

Q 

^ 

Q 

1  •       ' 

|             | 

H 

.H     | 

H 

H 

OJVolt  A.C.  CO  C 

ycles, 

-Main 

s  ^ 

1 

1 

1 

1 

/\ 

I 

1 

tn 

3  Volt  D.O.  CKI 

no,  -Mains  - 

d 

1 

1 

§ 

1 

>, 

0  Volt  A.C.  25  ( 

3yc)es 

-Mai 

ns<^ 

3 

2P^ase< 

1    1 

d 

3  Volt  A.C.  25  C 

jdles,-  Mai 

CQ 

| 

1 

d 

1 

1 

a 

D  Volt  D.  C.-  M 

insx 

-^ 

1 

1 

o 

i 

1 

Volt  A.C.  GO  C 

y(  lies  , 

Ma  r 

is<C 

1 

1 

03 

I 

1 

! 
i 

To  Tungsten 
Lamps 

1       j 

g 

*        1 

£     1 
1     f  1 

*To  Tungsten 
Lamps 

"*~To  Tungsten 

1      1 

3    5     1 
8     1 

r1  i 

"*~To  Tungsten 
Lamps 

<—  16-> 

"*~To  Tungsten 
Lamps 

il 
II 

CQ 

To  Tungsten 
Lamps 

FIG.  25.  —  Portion  of  typical  wiring  map  for  a  factory  aisle. 

section,  to  observe  the  illumination  effect.  If  unsatisfactory, 
or  if  any  modifications  are  required,  they  may  more  easily  be 
made  than  if  the  lamps  are  installed  as  a  whole  at  the  start. 

34.  Locating  the  Outlets  on  the  Ceiling. — Before  installing 
the  wires  and  hanging  the  lamps  it  is  well  to  chalk  out  the  loca- 
tion of  the  outlets  on  the  ceiling  according  to  the  working  draw- 
ing. At  this  juncture  the  engineer  will  find  'a  good  opportunity 
for  checking  over  the  drawing  in  terms  of  the  building  details. 
It  is  recommended  as  a  general  rule  that  all  locations  of  outlets 
in  new,  or  in  old  buildings  where  revisions  in  lighting  are  to  be 
made,  be  thus  chalked  out  prior  to  the  placing  of  wires,  in  order 
that  the  designer  may  have  a  chance  to  inspect  the  outlet  loca- 
tions in  relation  to  the  ceiling  construction  and  objects  to  be 
lighted. 


LIGHTING  INSTALLATION  WORK  45 

Where  stringer  boards  take  the  place  of  a  ceiling  in  the  over- 
head open  factory  girder  construction  for  supporting  the  lamps, 
these  boards  should  be  supported  rigidly  and  positively  to  the 
iron  work.  Lamp  trimmers  and  maintenance  men  will  support 
their  ladders  against  these  stringer  boards,  if  say  16  ft.  or  less 
above  the  floor,  and  the  physical  strength  of  these  boards  ought 
to  be  sufficient  to  permit  the  placing  of  a  ladder  against  them 
without  the  accidents  which  have  occurred  now  and  then  from 
the  giving  way  of  boards  fastened  insecurely. 

35.  Concluding  Items. — From  the  foregoing  an  idea  may  be 
gained  of  the  refinements  of  installing  lamps  systematically. 
Much  may  be  said  in  favor  of  instructing  the  wiring  foreman 
beforehand  as  to  the  importance  of  following  the  plans  accurately 
in  every  detail,  and  as  previously  intimated,  co-operation  be- 
tween the  wiring  foreman  and  the  designer  will  be  productive  of 
the  best  results. 

Factory  buildings  equipped  with  lighting  systems  based  on 
careful  plans,  and  where  the  installation  has  been  made  in  accord 
with  the  principles  just  explained,  present  not  only  a  pleasing 
appearance,  but  what  is  more  important,  they  furnish  to  the  plant 
equipment  a  distinct  asset  in  lower  maintenance  and  improved 
illumination  conditions,  which  are  valuable  in  their  relation  to 
the  general  efficiency  of  the  factory. 


CHAPTER  IV 


LIGHTING  MAINTENANCE  AND  MAINTENANCE 
RECORDS 

36.  Deterioration  of  Lighting  Equipment— Every  lighting 
system  suffers  deterioration  as  the  time  of  service  goes  on,  and 
unless  careful  attention  is  given  to  renewal  and  repair,  and  to 
other  features  involved  in  maintaining  highly  efficient  service, 
the  lighting  equipment  will  decrease  in  effectiveness. 

Systematic  maintenance  involves  attention  to  many  simple 
items.  In  fact  one  reason  for  the  gross  neglect  of  well  installed 
lighting  systems  in  some  instances  is  the  overlooking  of  these 
very  simple  features.  For  example,  the  accumulation  of  dirt  on 
the  surface  of  reflectors  or  globes  is  frequently  left  from  month 
to  month  simply  because  the  deterioration  of  light  which  the 
dirt  produces  may  be  so  gradual  as  to  be  scarcely  noticeable  to 
the  untrained  eye.  Where  lighting  systems  consist  of  a  number 
of  small  or  medium  sized  lamps,  those  which  become  dim  with 
age  or  even  lamps  which  have  burned  out  are  often  unnoticed  by 
the  maintenance  department  unless  regular  attention  is  directed 
to  items  of  this  kind. 

TABLE  VIII. — TEST  RESULTS  OBTAINED  UNDER  THE  SUPERVISION  OF  THE 
AUTHOR  TO  SHOW  LOSSES  DUE  TO  SOILED  LAMPS  AND  REFLECTORS 


Conditions  of  test 

Low 
office 

Fairly 
high 
factory 
office 

Low 

factory 
space 

Medium 
high 
factory 
space 

Fairly 
high 
factory 
space 

Ceiling  

Light. 

Light. 

Dark. 

Light. 

None. 

Walls  

Light. 

Light. 

None. 

Light. 

Dark. 

Lamps  

60-W.  Cl. 

60-W.  Cl. 

100-W.  Cl. 

100-W.  Cl. 

100-W.  Cl. 

Reflectors  

1-60  SF. 

1-60  Cl. 

1-100  Cl. 

1-100  Cl. 

F-100  Cl. 

Class  of  work  

Desk. 

Desk. 

Machines. 

Esnca. 

Bench. 

Time  between  washings  

14  weeks. 

17  weeks. 

9  weeks. 

11  weeks. 

13  weeks. 

Results 

Efficiency 

in  per  cent. 

Soiled  lamps  

19.7 

24.2 

22.4 

25 

20.1 

Soiled  reflectors. 

Clean  lamps  

20.7 

24.9 

22.5 

27 

23.6 

Soiled  reflectors. 

Clean  lamps 

34.  1 

29.3 

31.2 

35.3 

33.6 

Clean  reflectors. 

New  lamps  

34.1, 

31.2 

31.9 

36.1 

39.1 

Clean  reflectors. 

All  efficiency  values  corrected  for  normal  lamp  voltage. 

46 


LIGHTING  MAINTENANCE  AND  RECORDS 


47 


37.  Importance  of  Systematic  Maintenance. — The  necessity 
for  such  work  is  shown  by  the  large  losses  of  light  produced  by 
dirt  on  lamps  and  reflectors,  which  may  amount  to  as  much  as 
50  per  cent,  in  extreme  cases.  Its  importance  is  further  shown 
by  the  results  of  an  experiment  conducted  to  ascertain  how  bad 
this  deterioration  effect  may  be  in  a  practical  case,  as  shown  in 
Table  VIII,  the  results  of  this  test  corresponding  to  a  certain  de- 
gree of  neglect  in  the  proper  upkeep  of  the  systems  investigated. 

In  Fig.  26,  the  effect  is  shown  of  not  renewing  the  burned-out 
lamps  in  a  large  tungsten  lighting  system  on  certain  days.  In 


5  6 
t 

S    «*4 


9   10  11  12 

.'  ~   B 


14  15  16  17  18  19  20  21 

i  I 


FIG.  26. — Curve  showing  effect  on  number  of  lamps  to  be  renewed  when 
renewals  are  not  made  on  Saturday  and  Sunday  of  each  week.  Note  the 
peak  on  Monday  in  each  case  indicating  the  additional  lamps  burned  out 
since  the  last  renewal.  This  shows  that  lighting  conditions  become  very 
poor  if  the  lamps  are  not  renewed  regularly. 

the  short  interval  between  Friday  and  Monday  mornings  the 
number  of  lamps  burned  out  has  been  such  that  on  the  Monday 
mornings  following  these  intervals,  an  appreciably  larger  num- 
ber of  lamps  must  be  renewed  than  when  the  various  systems  are 
inspected  and  the  renewals  made  day  by  day. 

If  therefore  the  renewal  of  burned-out  lamps »is  neglected  for 
weeks  at  a  time,  such  systems  will  soon  be  practically  worthless 
as  efficient  light  producers,  and  where  large  sums  of  money  are 
expended  for  the  best  practical  illumination,  it  is  correspondingly 
important  for  those  in  charge  of  the  general  building  equipment 
to  properly  and  promptly  take  care  of  items  which  have  so  large 
an  influence  on  the  working  efficiency  of  the  employes. 

In  another  instance  several  tungsten  lighting  installations 
equipped  with  glass  reflectors  were  allowed  to  be  in  service  for 


48 


FACTORY  LIGHTING 


an  interval  of  several  weeks,  during  which  tests  were  made.  The 
results  of  these  tests  for  an  office  and  for  an  average  factory 
space  are  shown  in  Figs.  27  and  28.  The  office  in  question  was 
about  20  by  50  ft.  with  a  11-ft.  ceiling  and  walls  and  ceiling  of 
light  color.  The  factory  space  was  made  up  of  16  by  40  ft. 
bays  with  horizontal  roof  iron  work  16  ft.  above  the  floor,  and 
with  no  ceiling,  the  lamps  being  suspended  from  stringer  boards 
and  the  surroundings  very  dark,  although  with  not  a  great  deal 
of  dust  and  dirt  in  the  air.  It  should  be  stated  that  the  intervals 
between  cleanings,  as  carried  out  by  the  maintenance  department, 
were  14  weeks  in  the  office  and  13  weeks  in  the  factory  space. 


5.6 

4.8- 

|  4.0 

2  3.2 

•I2'4 

1 1.6 
0.8 


12 


18 


24          30          36 
Elapsed  Time  in  Days 


42 


48 


54 


FIG.  27.  —  Deterioration  curve  showing  effect  of  dust  and  dirt  accumula- 
tions on  glass  reflectors.       (Office.) 

Calculations  of  the  losses  in  light  at  a  fixed  cost  per  kilowatt- 
hour  show  in  Fig.  29  that  the  system  in  the  office  might  have 
been  thoroughly*  cleaned  at  intervals  of  4  weeks  instead  of  14, 
and  the  system  in  the  factory  space  might  have  been  cleaned  at 
intervals  of  less  than  2  weeks  instead  of  13,  at  an  expense  equal  to 
the  integrated  loss  of  light  between  cleaning  intervals  of  4  and  2 
weeks  respectively.  The  foregoing  tests  were  conducted  on  a 
large  number  of  lamps  in  practical  service. 

Another  evidence  of  the  losses  of  light  is  indicated  in  Fig.  30, 
which  shows  the  light  distribution  from  a  tungsten  lamp  and 
glass  reflector  before  and  after  cleaning,  the  unit  having  been  in 


LIGHTING  MAINTENANCE  AND  RECORDS 


49 


service  for  14  weeks  between  the  times  of  cleaning.  The  loss  of 
light  from  dirt  accumulations  in  this  case  amounted  to  40  per 
cent. 

In  this  last  case  if  we  interpret  into  cash  values  the  loss  of 
light  by  the  gradual  deterioration  of  the  reflector  and  lamp 
throughout  the  14  weeks,  it  will  be  found  on  certain  practical 
assumptions  that  the  part  of  the  energy  supplied  to  this  lamp 
which  was  wasted,  due  to  absorption  of  the  dirt  on  the  lamp  and 
reflector,  amounted  throughout  this  interval  to  27  cents,  while 
the  taking  down,  washing  and  replacing  of  the  reflector  amounted 


5.6 


4.8 


0.8 


\ 


12 


18          24          30  36 

Elapsed  Time  in  Days 


42 


48 


54 


FIG.  28. — Deterioration  curve  showing  effect  of  dust  and  dirt  accumula- 
tions on  glass  reflectors.     (Factory.) 

in  this  particular  location  to  but  3  cents.  Therefore,  if  the  illum- 
ination had  been  considered  sufficient  throughout  this  interval 
under  the  soiled  conditions,  it  is  obvious  that  considerably 
smaller  lamps  might  have  been  used  had  a  more  frequent  clean- 
ing interval  been  employed. 

38.  Cost  Relations  between  Maintenance  and  Losses  from 
Lack  of  Maintenance. — It  is  possible  to  use  a  larger  lamp  than 
necessary  at  the  start  provided  one  decides  that  the  lamps  will 
not  be  cleaned  for  a  very  long  interval;  or  a  smaller  lamp  may  be 
used  if  the  intervals  for  cleaning  are  sufficiently  short.  Based  on 
the  experiences  of  some  very  large  tungsten  installations,  it  may 
be  stated  as  an  illustration  that  in  planning  for  a  system  of 


50 


FACTORY  LIGHTING 


one  thousand  100- watt  tungsten  lamps  with  glass  reflectors,  the 
first  cost  will  amount  to  say  $4,000  on  certain  assumptions 
regarding  wiring  and  installation  expenses. 

If  the  lamps  and  accessories  are  cleaned  at  intervals  of  one 
month,  the  average  intensity  of  the  illumination  on  the  work 
throughout  the  interval  between  cleanings  will,  under  certain 
conditions,  be  about  3  foot-candles.  If,  on  the  other  hand, 
the  "system  were  not  cleaned  more  often  than  once  every  three 
months,  the  average  intensity  will  be  about  2.5  foot-candles 
in  certain  locations.  The  use  of  the  shorter  cleaning  interval 


tt  Cents  for  each 
Jten  Lamp 

co  ,u  **  ci 
to  o  co  c- 

Er 

era 

vat 

2C< 

Jilts 

pci 

Ki 

o\va 

tt-i 

:ou: 

/ 

/ 

/ 

/ 

/ 

Av 

Jl'Ut 

C  C 

3St  < 

f  C 

eaii 

ing: 

z 

3Cc 

nts 

J 

/ 

Losses  Due  to  Dirt  i 
100  -Watt  Tung 

0  f  N> 

bo  «  *» 

/ 

/ 

•V 

/ 

1 

/ 

,-° 

/ 

7 

2 

y 

z 

^ 

s 

/ 

^ 

/S 

J 

/ 

ji( 

sS 

S  ' 

sS 

/ 

*a> 

?» 

1  5  9  13          17          21          25          29          33         37 

Elapsed  Time  in  Days 

FIG.  29. — Curves  showing  the  losses  as  indicated  in  Figs.  27  and  28,  inter- 
preted into  kilowatt-hour  cost  equivalent. 

insures,  therefore,  in  this  case  a  resulting  average  intensity 
equal  to  20  per  cent,  more  than  where  the  longer  cleaning  inter- 
val is  employed. 

Taking  up  the  matter  in  further  detail,  it  is  apparent  that 
if  the  shorter  time  interval  is  decided  upon,  thus  producing  an 
average  intensity  as  shown  of  20  per  cent,  more  than  with  the 
longer  cleaning  interval,  the  number  of  lamps  in  the  original 
installation  might  have  been  cut  down  almost  16  per  cent.,  or  by 
an  amount  equal  to  about  $700  in  $4,000,  provided  the  lower 
average  intensity  was  considered  satisfactory.  In  other  words, 
to  the  factory  where  the  cleaning  of  extensive  lighting  systems 
is  given  no  attention  for  three  months  at  a  time,  it  may  be  stated 


LIGHTING  MAINTENANCE  AND  RECORDS          51 

that  by  cleaning  the  system  once  a  month,  if  the  conditions  are 
the  same  as  assumed  in  the  foregoing  illustration,  work  can  be 
performed  equally  well  either  with  lamps  approximately  16 
per  cent,  smaller  in  size,  or  with  a  system  composed  of  say  16  per 
cent,  less  lamps  than  the  system  in  question,  with  the  correspond- 
ing lower  first  cost  and  the  decrease  in  energy  consumption 
where  a  smaller  number  of  lamps  is  employed. 

The  percentages  just  given  will  obviously  be  larger  or  smaller 
depending  on  the  nature  of  the  location,  but  considerations  of 
this  kind,  although  hypothetical  in  a  degree,  are  instructive 
in  emphasizing  the  necessity  for  careful  attention  to  such  work.1 


90°i  JJ-^  on  AH/-I  90' 


15 


FIG.  30. — Distribution  curves  of  tungsten  lamp  and  reflector  before  and 
after  washing.  The  curve  obtained  after  washing  shows  that  40  per  cent,  of 
the  available  light  was  lost  by  absorption  when  the  reflector  was  soiled. 

39.  Items  Connected  with  the  Maintenance. — The  term  main- 
tenance as  used  in  connection  with  lighting  is  employed  in  a 
somewhat  liberal  sense.  It  is  intended  to  cover  the  general  work 
of  maintaining  highly  efficient  illumination  and  therefore  com- 
prehends all  items  bearing  on  efficient  lighting  service. 

Tungsten  Lamps. — In  the  case  of  tungsten  lamps,  for  example, 
it  is  necessary  after  the  system  has  been  installed  to  renew  all 
burned  out,  broken  or  missing  lamps;  to  renew  broken  or  damaged 
reflectors;  and  to  clean  the  lamps  when  soiled  and  to  remove  and 
wash  thoroughly  the  reflectors  when  the  accumulations  of  dust  and 
dirt  warrant.  The  items  mentioned  include  both  labor  and 
material  costs  and  are  summarized  in  Table  IX,  which  indicates 

1  See  paper  by  the  author  on  "Industrial  Illumination  and  the  Average 
Performance  of  Lighting  Systems,"  Transactions  American  Institute  of 
Electrical  Engineers,  Vol.  XXXI,  June,  1912. 


52  FACTORY  LIGHTING 

* 

the  components  of  tungsten  maintenance.  The  costs  connected 
with  wiring  repair  are  not  included  since  they  fall  naturally  under 
the  head  of  wiring  upkeep.1 

TABLE  IX. — TABLE  OF  MAINTENANCE  ITEMS  FOR  TUNGSTEN  LAMPS 

Item  Item 

Cost  of  power  for  month.  Labor  on  reflector  washing. 

Cost  of  renewal  of  lamps.  Labor  on  reflector  screening. 

Cost  of  reflectors  broken.  Over-head  expense. 

Labor  on  lamp  and  reflector  renewals.  Total. 

Arc  Lamps. — In  like  manner,  the  various  items  connected  with 
the  upkeep  of  arc  lamps  include  the  labor  and  material  for  trim- 
ming the  lamps,  renewing  globes  and  reflectors,  incidental  repairs 
on  the  lamps,  and  washing  the  globes  and  reflectors.  These 
items  are  shown  in  Table  X. 

TABLE  X. — TABLE  OF  MAINTENANCE  ITEMS  FOR  ARC  LAMPS 

Item  Item 

Cost  of  power  for  month.  Labor  on  lamp  repairs. 

Cost  of  carbons.  Labor  on  lamp  trimming. 

Cost  of  globes  broken.  Labor  on  globe  washing  and  screening 

Cost  of  repair  parts.  Overhead  expense. 

Total. 

Other  Lamps. — In  a  similar  manner,  the  items  connected  with 
the  maintenance  of  other  types  of  lamps  may  be  enumerated  and 
in  a  subsequent  article,  under  the  head  of  maintenance  records, 
they  will  be  considered  more  at  length. 

40.  Inspecting  Lighting  Systems. — Formerly  the  matter  of 
looking  after  lamps  and  accessories  was  usually  delegated  to  the 
repair  man,  who  was  sent  out  from  the  repair  room  from  time 
to  time  to  investigate  wiring  difficulties.  In  fact,  it  has  not 
been  a  matter  of  such  great  importance  regularly  to  inspect 
lamps  and  auxiliaries  in  the  past  as  is  the  case  to-day  for  two 
reasons.  First,  a  larger  variety  of  lamps  is  in  use  now  than 
formerly  and  often  a  large  number  of  medium-sized  lamps  is  in 
service;  second,  the  greater  appreciation  for  efficient  illumi- 
nation has  caused  a  great  demand  for  a  more  liberal  use  of  lamps 
than  formerly. 

1  See  paper  by  the  author  on  "  Report  Submitted  by  the  Illuminating 
Engineering  Department  of  the  Westinghouse  Electric  and  Manufacturing 
Company,"  Transactions  National  Electric  Light  Association,  May  29  to 
June  2,  1911. 


LIGHTING  MAINTENANCE  AND  RECORDS 


53 


Experiences  in  the  immediate  past  in  the  formation  of  an 
inspection  division  have  shown  that  in  the  average  factory  a 
distinctly  new  division  in  the  organization  of  the  lamp  depart- 
ment is  required  to  include  regular  inspections  of  the  lighting 
equipment.  The  development  of  the  inspection  division  in  a 
typical  factory  has  shown  several  interesting  features  which  are 
subsequently  described  with  particular  reference  to  installations 
of  small  or  medium-sized  over-head  lamps. 

The  floor  space  of  the  factory  in  question  was  divided  into 
sections,  each  of  which  is  covered  by  an  inspector  early  on  each 
morning  and  according  to  a  definite  route  as  shown  in  Fig.  31. 


200  Feet 


FIG.  31. — Typical  inspection  route  in   a  factory. 


It  is  the  duty  of  the  inspector  to  follow  this  route  and  to  indi- 
cate as  he  proceeds  the  location  of  burned-out  lamps,  as  well 
as  the  lamps  which  have  deteriorated  due  to  life  limit  or  to  dirt 
accumulations,  also  lamps  which  have  been  removed  from  the 
sockets,  loose  or  broken  switches,  imperfect  fuse  connections, 
and  similar  items.  If  the  lamps  are  not  burning,  it  is  his  duty  to 
turn  them  on  and  to  make  sure  that  all  are  in  good  working 
order. 

Judgment  must  be  exercised  by  such  an  inspector  to  detect 
accumulations  of  dirt  and  dust  which  may  be  such  as  to  cause  the 
lamps  on  a  given  day  to  have  reached  a"  condition  of  unsatis- 
factory service.  One  of  the  most  difficult  things  in  the  main- 


54  FACTORY  LIGHTING 

tenance  and  inspection  work  is  to  appreciate  fully  the  degree  of 
dirt  deterioration  of  lamps  and  their  auxiliaries. 

Thus,  reflectors  in  the  factory  or  in  the  office  which  may  appear 
clean  when  not  compared  with  other  reflectors  which  are  clean, 
may  be  soiled  in  a  degree  which  is  difficult  to  realize  until  the 
dirt  has  been  removed.  It  is  a  common  occurrence  in  passing 
under  a  large  number  of  over-head  lamps  after  a  casual  observa- 
tion, to  feel  that  they  are  in  good  shape.  After  turning  off  the 
lamps,  however,  and  cleaning  one  lamp  and  its  reflector,  the 
comparison  between  the  clean  lamp  and  the  others  will  often 
show  remarkable  differences,  which  sometimes  aggregate  40 
and  even  50  per  cent,  in  light. 

As  the  inspection  is  made,  a  record  must  be  prepared  which 
indicates  the  locations  at  which  the  burned  out  or  otherwise 
defective  lamps  are  to  be  found.  Upon  the  completion  of  the 
inspection  the  report  is  made  up  into  concise  form  and  turned 
over  to  the  maintenance  division  after  which  the  necessary 
renewals  and  repairs  are  made,  preferably  on  the  same  day.  In 
following  such  a  course  it  should  be  kept  in  mind  that  one 
lamp  out  may  affect  the  work  of  a  man  to  a  degree  far  in  excess 
of  the  cost  of  quickly  and  effectively  remedying  the  bad  lamp. 
When  looked  at  from  the  standpoint  of  production  working 
results  as  affected  by  the  lighting,  the  labor  and  effort  both  of 
the  inspection  and  the  prompt  action  following  the  inspection 
become  insignificant  in  the  matter  of  relative  cost. 

A  common  form  of  inspection  report  is  shown  in  Fig.  32, 
where  the  first  portion  of  the  figure  indicates  the  inspector's 
report  made  up  immediately  after  the  completion  of  the  rounds. 
The  second  portion  indicates  the  carbon  copy  of  the  original 
report,  which  is  returned  to  the  inspection  division  after  all  the 
lamps  reported  have  been  renewed.  When  the  renewal  man 
ascertains  that  a  certain  lamp  reported  as  burned  out  is  not  a 
defective  lamp  but  is  perhaps  loose  in  the  socket,  he  checks  off 
the  item  on  the  report  after  placing  the  lamp  in  service.  The 
inspection  division  is  furnished  in  this  way  with  an  accurate 
record  of  the  number  of  lamps  renewed  and  this  record  may  be 
used  at  the  end  of  each  month  to  form  a  complete  report  on 
maintenance  costs.  In  some  instances  it  is  possible  with  the 
force  available  to  complete  the  inspection  by  ten  or  eleven 
o'clock  in  the  morning,  and  by  a  short  time  after  the  noon  hour 
to  have  all  lamps  in  working  order. 


LIGHTING  MAINTENANCE  AND  RECORDS 


55 


One  of  the  important  points  connected  with  such  inspection 
work  is  to  indicate  in  a  clear  manner  for  the  renewal  man,  the 
location  of  the  defective  lamps  so  as  to  avoid  delays  in  finding 
the  same.  This  is  done  to  the  best  advantage  by  specifying 


Or/g/naf  Copy 


Date  6-/9-S2.. 


LOCATION 


STYLE 


OUT 


BLK 


FUSE 


MISS 


NOTES 


6-7 


/7 


46-17 


Carbon  Copy 


Date  6- 


LOCATION  ~tftfkre") 
(Shop  ) 


STYLE 


OUT 


BLK 


FUSE 


MISS 


NOTES 


.  £- 


I/ 


6-7 


I/ 


/  7 


-^  7 


ff-/ 


z-/ 


FIG.  32. — Inspection  reports  before  and  after  the  day's  work  in  the  main- 
tenance department. 


the  exact  location  between  column  numbers,  and  to  this  end 
the  various  columns  or  bays  throughout  the  factory  should  be 
numbered  to  facilitate  work  of  this  kind  as  well  as  many  other 
branches  of  the  general  upkeep  work. 


56 


FACTORY  LIGHTING 


41.  Cleaning  Reflectors  and  Globes. — It  should  be  the  duty 
of  inspectors  to  report  promptly  all  lighting  equipment  in  need 
of  cleaning.  In  some  instances  it  may  be  practicable  for  the 
lamp  renewal  man  himself  to  undertake  the  cleaning  of  glassware 
or  reflectors.  For  example,  the  arc  lamp  trimmer  can  brush  out 
the  globes  from  time  to  time  when  renewing  the  carbons  or 
electrodes. 

In  many  cases,  however,  as  with  the  glass  reflectors  for  tung- 
sten lamps,  it  is  necessary  to  make  the  cleaning  of  reflectors 


FIG.  33. — Truck  used  for  maintenance  of  reflectors  in  tungsten  systems. 

a  distinctly  separate  part  of  the  work.  It  is  a  good  thing  to 
have  a  regular  schedule  for  cleaning  the  various  lamp  auxiliaries, 
but  such  a  schedule  must  often  necessarily  be  supplemented  by 
a  regular  inspection.  At  first  thought  it  may  appear  an  almost 
impossible  problem  to  handle  thousands  of  glass  reflectors  used 
with  tungsten  lamps,  but  this  work  like  all  other  maintenance 
work  can  be  reduced  to  a  systematic  basis. 

In  some  large  factories  a  special  washing  division  has  been 
located  in  the  lamp  department,  to  which  point  all  the  dirty 
reflectors  are  removed  for  cleaning.  In  factories  where  the 
floor  space  is  under  one  roof,  the  reflectors  may  be  removed 


LIGHTING  MAINTENANCE  AND  RECORDS          57 


from  the  various  installations  to  this  central  washing  point  on 
a  specially  prepared  truck  as  shown  in  Fig.  33.  In  this  case, 
when  an  installation  requires  washing,  the  reflectors  are  taken 
down  one  at  a  time  and  clean  reflectors  which  have  been  hauled 
out  on  the  truck  are  at  once  installed.  The  dirty  reflectors 
being  loaded  in  turn  on  the  truck  are  returned  to  the  washing 
station,  where  they  are  washed, 
dried  and  returned  to  stock  ready 
for  future  use. 

Difficulties  are  sometimes  en- 
countered in  removing  reflectors. 
In  some  cases  the  lamps  are  ac- 
cessible only  from  the  top  of  a 
crane  or  from  the  sides  of  galler- 
ies, and  hence  two  men  are  gen- 
erally needed  to  carry  on  the 
work  successfully.  One  of  these 
men  removes  the  reflector  while 
the  other  receives  the  dirty  unit 
and  hands  up  a  clean  one  thus 
facilitating  the  handling  of  the 
glassware. 

If  the  lighting  installations 
are  small,  the  renewal  reflectors 
may  be  carried  from  place  to 
place  on  small  hand  racks  as 
shown  in  Fig.  34,  this  obviating 
the  necessity  of  a  truck.  Here 
the  reflectors  are  placed  over 
the  rod  after  the  removal  of  the 
handle  at  the  top  of  the  rack, 
after  which  the  handle  is  inserted 

and  the  rack  is  ready  for  use.  Fig.  35  shows  a  simple  washing 
trough  with  supporting  surfaces  for  dirty  reflectors  and  drain 
boards  for  those  which  have  been  washed. 

42.  Maintenance  Records. — The  need  is  keenly  felt  for  a 
standard  scheme  which  will  make  possible  the  accurate  account- 
ing of  the  costs  of  factory  lighting  systems.  On  the  one  hand, 
the  operating  man  desires  to  know  definitely  how  much  the 
operation  and  maintenance  cost  of  every  part  of  his  factory 
equipment  amounts  to,  and  also  how  it  compares  with  similar 


FIG.  34. — Hand  rack  for  carry- 
ing glass  reflectors. 


58 


FACTORY  LIGHTING 


costs  in  other  plants;  on  the  other  hand,  the  man  who  contem- 
plates the  purchase  of  new  lighting  apparatus  desires  a  standard 
basis  on  which  to  compare  the  many  types  of  lamps  now  avail- 
able. Simple  as  these  two  viewpoints  may  appear,  they  include 
probably  the  most  discussed  items  connected  with  the  whole 
practical  lighting  field. 

For  the  purpose  of  laying  stress  on  the  importance  of  system- 
atically recording  lighting  maintenance  items,  and  also  for 
advancing  general  interest  and  adherence  to  certain  set  forms  for 
such  records,  the  subsequent  paragraphs  are  presented. 


FIG.  35. — Washing  trough  used  for  cleaning  glass  reflectors  and  globes. 

43.  Items  Included  in  the  Lighting  System. — A  definite  record 
of  each  group  of  lamps  throughout  the  factory  should  be  on  file. 
This  record  should  contain  the  boundaries  of  each  location,  the 
type  of  lamp  and  its  auxiliary  reflector  or  globe,  the  type  of 
holder  which  supports  the  reflector,  or  globe,  the  spacing  distance 
and  mounting  height  of  the  lamps,  and  the  height  of  the  ceiling 
or  iron  work  of  the  building.  This  information  may  be  tabulated 
on  a  chart  as  shown  in  Fig.  36,  and  it  should  be  kept  up  to 
date  for  use.  as  a  ready  reference  by  lamp  trimmers  and  main- 
tenance men. 


LIGHTING  MAINTENANCE  AND  RECORDS 


59 


The  preparation  and  maintaining  of  a  record  of  this  kind 
is  a  valuable  item  in  every  factory  whether  small  or  large,  but 
its  importance  increases  with  the  size  of  the  factory.  This  rec- 
ord will  indicate  first  the  exact  nature  of  the  lighting  equipment 
when  taking  stock  of  the  various  kinds  of  apparatus  in  the  plant ; 
second,  it  serves  as  a  basis  for  maintenance  records  from  month 
to  month;  and  third,  it  is  a  guide  to  inspectors  in  keeping  their 
rounds  up  to  date  when  needed  revisions  are  necessary  to  accom- 
modate additions  to  the  factory. 

A  record  as  just  described  is  comparatively  simple  if  one 
type  of  lamp  only  is  in  service.  Where  many  types  of  lamps  are 
used  in  a  great  variety  of  groups  throughout  the  buildings,  the 


Location 

Lamp 

Reflector  koideij 

Ceiling 
Height 

Mounting 
Height 

Spacing 
Distance 

Watts  per 
Square  Ft. 

No. 

Type 

Size 

Volts 

Bize 

T,p« 

_ 

FIG.  36. — Table  of  information  of  tungsten  systems  in  a  factory  used  by 
maintenance  department  for  ready  reference. 

records  become  somewhat  more  difficult,  but  they  are  of  greater 
importance  in  the  latter  case  than  in  the  former.  Although  a 
large  chart  has  been  suggested  by  Fig.  36,  the  records  may  also 
be  kept  to  advantage  in  a  blank  book,  at  the  top  of  the  pages  of 
which  the  various  types  of  lamps  are  indicated,  and  the  spaces 
below  these  headings  may  be  used  for  recording  the  maintenance 
items  from  time  to  time. 

44.  Record  Charts. — It  is  highly  desirable  to  make  use  of 
regularly  prepared  charts  for  recording  the  various  maintenance 
items  from  month  to  month.  Charts  for  the  tungsten,  arc  and 
mercury  vapor  lamps  are  shown  in  Figs.  37,  38,  and  39.  It  is 
advisable  at  the  end  of  each  month  to  incorporate  on  these  charts 
the  tabulated  items  in  all  the  divisions  of  the  lighting  service 
for  each  type  of  lamp.  At  the  end  of  a  year  a  comparison  of  the 
monthly  values  indicates  in  a  certain  manner  whether  some  of 
the  items  are  running  higher  than  normal,  and  shows  the  differ- 
ence between  winter  and  summer  conditions. 

Such  records  are  valuable  to  the  operating  man  in  connection 
with  his  plant  at  any  given  time,  and  they  form  a  practical 


60 


FACTORY  LIGHTING 


Monthly  Tungsten  Lamp  Maintenance  1912. 

5 

Number  of  Lamps 
Installed 

Kilowatt  Hours  for 
Entire  Month  Assuming 
9  Hours  per  Day  Service 

1  Total  Lamps 
Burned  out 

Total  Lamps 
Blackened 

r  Total  Lamps 
Missing 

Total  Renewals: 
all  Sizes 

Material 

Labor 

Over  Head 
Expense 

D 
I 

•3g« 

¥ 

c3 
S 

Maintenance  Cost 
per  Kilowatt 
Hour 

Maintenance  per  Month 
per  1000  Sq.  Ft.  per 
2U.8U  F.O. 

^ 

Vfc 

1*1 

fi 

st 

<sls 

ill 

fyp 

Cost  of  Broken 
Reflectors 

*H 

•as 

g§« 

flSaJ 

|3M 

Reflector 
Washing 

Reflector 
Screening 

1911 

Average 

January 

February 

March 

April 

May 

June 

July 

August 

September 

October 

November 

December 

FIG.  37. — Record  blank  for  monthly  maintenance  of  tungsten  systems. 


Monthly  Arc  Lamp  Maintenance  1912. 

Month 

No.  of  Lamps 

Kilowatt  Hours  for  Entire 

Month,  Assuming  2J4 
Kilowatt  Hours  per  Carbon 

No.  of  Carbons 

£ 

J3 
o 

3 

"S 

d 
ft 

Material 

Labor 

Over  Head 
Expense 

Total  Maintenance 
Cost 

Maintenance 
Cost  per  K.W.H. 

Maintenance  Cost  per 
Month  perl  000  Sq.  Ft. 
per  2^-3%  F.C. 

Maintenance  Cost 
per  Lamp  per 
Month 

°l 
I| 

Cost  of 
Globes 

Cost  of  other 
Renewals 

!J 

Lamp 
Trimming 

Is 

III 

e1l 
£ 

Avl^ge 

January 

February 

March 

April 

May 

June 

July 

August 

September 

October 

November 

December 

FIG.  38. — Record  blank  for  monthly  maintenance  of  arc-lamp  system. 


LIGHTING  MAINTENANCE  AND  RECORDS 


61 


basis  of  comparison  between  various  types  of  lamps,  whether 
conclusions  must  be  reached  on  existing  installations,  or  whether 
decisions  are  to  be  made  in  connection  with  anticipated  exten- 
sions with  new  lighting  equipment. 

It  is  urgently  recommended  that  attention  be  directed  to 
records  of  this  kind  and  that  co-operation  between  the  manufac- 
turers of  lamps  and  factory  operators  be  realized  as  a  part  of  the 
work  connected  with  a  broader  intelligence  along  the  lines  of 
maintenance  values  than  has  hitherto  been  possible. 


Monthly  Mercury  Vapor  Lamp  Maintenance  1912. 

Month 

h 

t-l    a 

•H    » 
°.    « 

0    M 

H 

«2££ 

|f 

Wofrg 

fill 
Is! 

• 

l! 
P 

Material 

Labor 

«  3 

"I 
j* 

CD 

w 

3|t8 

o  »  o 
Ha° 

- 

°3 

Us 

IV 

a 
% 

8 

0  *nH 

Maintenance  Cost 
per  Lamp  per 
Month 

Cost  of 
Renewals 

Lamp  Repair 
and 
Trimming 

Lamp 
Renewing 

a    | 

9   "a 

3  3 
5 

^Sd 

O-fl-wfjJ 

Hi 

*%n*? 

PS 

AvWlge 

January 

February 

March 

April 

May 

June 

July 

August 

September 

October 

November 

December 

FIG.  39. — Record  blank  for  monthly  maintenance  of  mercury  vapor  lamp 

systems. 

45.  Simplicity  Essential. — It  is  not  the  intention  to  set  forth 
the  work  connected  with  maintenance  and  maintenance  records 
as  complicated  or  intangible.  As  a  fact,  work  of  this  kind  is 
exceedingly  simple,  and  its  complexity  is  apparent  only  in  the 
light  of  its  having  been  a  neglected  matter  in  many  factories  in 
the  past.  Judgment  and  common  sense  will  do  more  than  set 
rules,  after  those  involved  become  aware  of  the  importance  of 
the  subject. 

The  methods  just  described  and  the  accompanying  principles 
of  procedure  are  intended  to  be  somewhat  suggestive.  They 
may,  therefore,  be  used  as  a  guide  in  undertaking  such  work  for 


62  FACTORY  LIGHTING 

the  first  time.  Much  individuality  must,  however,  of  necessity 
enter  into  each  separate  case,  and  the  modifying  of  certain  points 
here  and  there  to  suit  the  conditions  should  make  the  different 
ideas  which  have  been  set  forth  adaptable  to  practically  every 
factory. 

46.  Storage. — The  store-rooms  in  a  maintenance  division  are 
often  an  index  into  the  efficiency  with  which  it  is  operated.     In 
those  cases  where  the  shelves  are  neatly  filled  with  carefully 
divided  classes  of  material,  one  may  roughly  conclude  that  the 
entire  department  is  run  on  a  systematic  basis.     On  the  other 
hand,   where  confusion  pervails  in  the  store-room,  it  is  almost 
obvious  that  conditions  in  the  work  are  not  what  they  should 
be.    Jt  is  apparent  that  to  facilitate  the  maintenance,  system 
and  care  in  the  handling  of  materials  in  the  store-room  are  re- 
quired, as  well  as  in  the  recording  of  each  item  of  material  which 
is  given  out. 

With  modern  lighting,  one  tendency  will  be  to  use  large  va- 
rieties of  types  of  lamps  on  account  of  the  comparatively  large 
number  of  kinds  of  lamps  on  the  market.  This  tendency  to 
diversified  types  of  lamps  will  include  also  a  corresponding 
variety  of  reflectors  and  other  accessories  on  the  market.  Hence, 
it  is  suggested  that  all  branches  of  the  factory  lighting  equip- 
ment be  limited  to  as  few  types  as  is  consistent  with  excellence 
of  service. 

It  is  recommended  further  that  standards  be  made  for  the 
items  connected  with  the  lighting  equipment,  not  only  to 
facilitate  the  work  of  maintenance  by  avoiding  confusion  apt  to 
result  from  too  large  a  number  of  types  of  accessories,  but  also 
for  making  possible  a  more  accurate  recording  of  the  maintenance 
in  their  use. 

47.  Results  of  Adherence  to  These  Principles. — One  notice- 
able defect  in  the  records  of  maintenance  in  many  factories  is 
the  lack  of  separation  of  the  different  items.     For  example,  the 
entire  upkeep  expense  for  lighting  may  be  summed  up  as  one 
total,  while  the  cost  for  heating  may  be  summed  up  as  another 
total,  and  the  cost  for  ventilation  as  another.     The  combination 
of  all  these  items  into  one  total  for  the  entire  shop  maintenance 
is  unfortunate  in  as  far  as  it  renders  the  comparison  of  upkeep 
costs  of  various  types  of  lamps  impossible  for  the  different 
locations  throughout  the  factory.     One  of  the  main  difficulties 
in  the  way  of  a  suitable  separation  of  costs  is  in  the  labor  charges, 


LIGHTING  MAINTENANCE  AND  RECORDS          63 

particularly  for  men  who  are  employed  to  take  care  of  the  main- 
tenance of  lighting  equipment  together  with  other  allied  work. 

Care  in  the  matter  of  instructing  the  workmen  as  to  recording 
their  time  will  permit  of  the  proper  apportionment  of  charges  for 
each  branch  of  the  lighting  equipment,  and  the  trouble  connected 
with  this  separation,  particularly  in  large  plants,  is  more  than 
compensated  for  by  the  satisfaction  of  knowing  how  the  depart- 
ment is  being  conducted  and  how  the  costs  vary  from  month  to 
month. 

Where  these  methods  have  not  been  employed  in  the  past,  shop 
owners  and  others  have  often  come  to  entirely  incorrect  conclu- 
sions regarding  the  costs  for  artificial  illumination,  and  upon 
the  requirement  of  new  equipment  they  are  at  a  loss  to  know 
with  certainty  the  relative  merits  of  the  various  systems  under 
consideration. 

With  all  that  has  been  stated,  however,  a  proper  distinction 
should  be  kept  in  mind  between  what  may  be  termed  the  cost  and 
value  of  light.  All  results  secured  through  the  adoption  of  a 
maintenance  record  system  as  just  described  must  be  interpreted 
with  judgment.  The  value  of  the  illumination  best  suited  to  the 
various  kinds  of  work  as  an  aid  to  output,  should  receive  greater 
attention  than  small  differences  in  cost.  These  differences  in 
cost  should  be  used  as  a  basis  of  comparison  only  providing  such 
differences  do  not  entail  any  sacrifices  one  way  or  another  in  the 
illumination  facilities.  It  is  believed,  however,  that  the  prac- 
tical man  will  see  the  balance  between  costs  and  illumination 
results  in  such  a  way  that  the  adoption  of  a  systematic  method  of 
recording  maintenance  will  be  productive  not  only  of  greater 
satisfaction  to  those  involved,  but  will  serve  to  aid  in  a  realization 
of  definite  standards  of  comparison  between  various  types  of 
lamps  which  may  be  used  for  given  classes  of  work. 

It  is  well  to  note  that  a  high  maintenance  as  shown  by  these 
records  may  not  always  indicate  an  inferior  type  of  lamp,  but  in 
the  case  of  very  old  systems  where  the  lamps  have  been  in  service 
for  years,  the  high  maintenance  of  equipment  may  indicate  that 
the  lamps,  although  originally  efficient  and  satisfactory,  have 
reached  a  natural  age  limit  and  should  be  replaced  with  improved 
apparatus.  This  is  obviously  a  point  of  advantage,  because  the 
fact  that  a  lighting  system  is  old  and  antiquated  is  hardly  ever 
brought  home  with  such  force  as  when  the  actual  outlay  for  main- 
tenance is  seen  to  have  reached  excessive  values. 


64  FACTORY  LIGHTING 

Data  obtained  from  actual  records  is  much  more  reliable 
provided  the  conditions  surrounding  the  lighting  installation 
are  given  due  weight,  in  reaching  conclusions  connected  with 
operation  and  maintenance  costs,  than  mere  general  statements 
which  are  often  dependent  upon  assumed  values  or  indefinite 
information.  Those  who  are  equipped,  therefore,  with  definite 
facts  save  themselves  much  unnecessary  argument,  and  have 
information  available  which  permits  intelligent  conclusions 
through  the  medium  of  actual  experience. 


CHAPTER  V 
OFFICE  LIGHTING 

48.  General  Items. — The  adequate  illumination  of  the  office 
presents  problems  materially  different  from  those  pertaining  to 
the  majority  of  industrial  situations.     In  the  treatment  of  this 
subject,  offices  containing  a  number  of  desks  will  be  considered 
in  the  main.     Two  methods  may  be  used  for  furnishing  artificial 
light  to  the  desk  surfaces,  first,  individual  lamps  may  be  located 
over  and  close  to  the  surface  of  each  desk,  with  a  small  amount  of 
general  illumination  from  over-head  lamps;  second,  the  lamps 
may  all  be  arranged  over-head  in  such  a  way  and  in  such  numbers 
as  to  produce  a  satisfactory  amount  of  illumination  on  the  desk 
surfaces  without  the  use  of  individual  lamps. 

The  latter  method  has  many  advantages.  It  is  desirable  in 
many  practical  office  locations  to  install  the  lighting  system  so 
that  the  illumination  may  be  satisfactory  irrespective  of  changes 
in  the  arrangement  of  desks  or  files.  Individual  lamps  when 
located  close  to  the  desks  must  be  moved  with  each  readjustment 
of  the  desks,  and  in  large  office  buildings  this  is  likely  to  increase 
the  maintenance  expense  considerably.  As  a  starting-point, 
therefore,  it  is  assumed  that  satisfactory  office  lighting  involves 
the  furnishing  of  adequate  light  in  all  parts  of  the  office  somewhat 
independent  of  the  location  of  the  desks. 

49.  General  Requirements  based  on  the  Foregoing  Considera- 
tions.— The    general    requirements   for    office   lighting  may  be 
summed  up  as  follows: 

(1)  Sufficient  illumination  for  each  person  in  the  office. 

(2)  An  arrangement  of  lamps  which   produces   satisfactory 
illumination  without  regard  to  the  arrangement  of  desks. 

(3)  An  installation  of  lamps  which  will  avoid  eye  strain. 

(4)  A  selection  of  the  type  of  lamp  adapted  to  each  size  of 
office  and  to  the  various  kinds  of  work  performed. 

Numerous  investigations  have  shown  the  harmful  effect  on  the 

eye,  and  the  inconvenience  resulting  from  the  continuous  use  of 

a  single  lamp  placed  directly  over  and  close  to  the  desk  surface, 

since  the  light  from  the  individual  lamp  is  apt  to  be  too  strong 

5  65 


66 


FACTORY  LIGHTING 


and  to  give  reflection  from  paper  surfaces.  This  effect  is  possi- 
bly overlooked  by  the  average  person,  who  has  been  accustomed 
to  use  such  a  lamp,  but  a  little  observation  will  indicate  that  the 
bright  spot  of  light  directly  under  the  lamp  is  generally  sur- 
rounded by  a  region  of  comparative  darkness,  causing  the  eye  to 
suffer  from  a  possibly  excessive  intensity  of  this  bright  spot,  and 


T 


i 


Elevation 
20'- 


C 


C 


a- 


Plan 

FIG.  40. — Plan  and  elevation  of  test  office  showing  original  lighting 
arrangement.  Center  lamp  300  candle-power,  carbon  filament  lamps  at 
the  sides  of  room. 


to  become  fatigued  from  the  continual  changing  of  the  line  of 
vision  from  the  bright  area  under  the  lamp  to  the  comparatively 
dark  surroundings.  This  strain  on  the  eye  is  largely  avoided  if  the 
desk  surface  is  provided  with  a  uniform  illumination  of  moderate 
intensity. 

50.  A  Typical  Office  Investigated. — In  order  to  determine 


OFFICE  LIGHTING  67 

the  various  factors  connected  with  satisfactory  illumination 
under  office  conditions,  tests  were  conducted  in  what  may  be 
considered  a  typical  office,  20  ft.  square  and  with  a  ceiling  height 
of  11  ft.  6  in.  A  floor  plan  and  elevation  are  shown  in  Fig.  40. 
This  typical  office  contains  five  desks  arranged  as  indicated  in 
the  illustration,  is  occupied  by  six  persons,  and  under  the  old 
scheme  of  lighting,  it  was  equipped  with  one  large  lamp  in  the 
center  of  the  ceiling,  and  four  individual  carbon  filament  lamps 
immediately  over  the  desks  located  directly  against  the  walls. 

Various  complaints  were  made  as  to  the  artificial  illumination 
in  this  particular  office,  and  the  investigation  of  these  complaints 
shows  that  they  may  be  classed  under  three  heads  as  follows: 

(1)  The  surfaces  of  the  desks  were  not  uniformly  illuminated 
by  the  over-head  lamp,  particularly  along  the  walls,  thus  requir- 
ing individual  desk  lamps. 

(2)  Those  persons  facing  or  partially  facing  the  large  lamp  at 
the  center  of  the  ceiling  were  affected  by  the  intrinsic  brightness 
of  the  lamp,  as  well  as  the  reflection  from  glossy  papers  on  the 
desks,  resulting  in  excessive  eye  strain  and  even  headaches  to 
certain  persons. 

(3)  The  desks  located  along  the  walls  being  occupied  by  per- 
sons who  faced  the  wall,  were  in  a  shadow  from  the  over-head 
lamp  and  were,  furthermore,  not  uniformly  illuminated  by  the 
desk  lamps.     The  desk  surfaces  were  therefore  too  bright  directly 
below  the  individual  lamp,   and  comparatively  dark  in  other 
portions. 

The  attempt  was  made  to  solve  these  difficulties  and  to  fulfil 
the  general  requirements  as  outlined  in  the  preceding  article, 
through  lamps  mounted  over-head  and  through  the  removal  of 
the  various  individual  lamps  over  the  desks  near  the  walls. 

Various  Schemes  given  Trial. — The  first  step  was  the  installa- 
tion of  four  lamps  somewhat  smaller  than  the  large  lamp  at  the 
center  of  the  ceiling,  these  lamps  being  arranged  over-head  as 
shown  in  Fig.  41.  The  two  types  of  lamps  available  for  this 
scheme  were  tried  consecutively  and  it  was  found  that  the  side 
desks  still  required  individual  lamps.  The  over-head  units 
being  located  in  a  symmetrical  manner  with  regard  to  the  floor 
space,  furnished  fairly  uniform  illumination  for  the  central  por- 
tions of  the  room,  without  adequately  illuminating  the  desks 
along  the  walls. 

This  plan  does  not,  therefore,  fulfil  the  general  requirements 


68 


FACTORY  LIGHTING 


as  previously  outlined  because,  first,  a  change  in  the  location  of 
wall  desks  involves  a  shifting  of  the  individual  lamps,  and  second, 
because  the  size  of  the  four  over-head  lamps,  while  sufficiently 
large  to  provide  adequate  illumination,  results  in  units  of  candle- 
power  large  enough  to  produce  very  appreciable  eye  strain  to 
those  persons  facing  or  partially  facing  the  four  over-head  lamps. 


Elevation 
20 


Plan 

FIG.  41. — Plan  and  elevation  of  test  office  showing  first  trial  for  improve- 
ment of  the  lighting.     100-watt  (80  candle-power)  tungsten  lamps  used. 

Five  lamps  on  the  ceiling  according  to  Fig.  42  were  then  given 
trial  in  the  hope  that  the  additional  central  unit  would  permit  of 
moving  the  four  outside  corner  lamps  closer  to  the  walls,  thus 
increasing  the  illumination  on  the  outer  desks  and  eliminating  the 
necessity  for  individual  lamps.  The  increase  in  the  total  number 
of  lamps  made  possible  a  slight  reduction  in  the  candle-power  of 
each  lamp,  but  the  eye  strain  produced  on  those  who  received  the 


OFFICE  LIGHTING 


69 


direct  rays  from  over-head  lamps  was  still  pronounced  excessive 
after  a  considerable  time  of  service.  The  resulting  intensity  on 
the  outer  desks  was  still  insufficient  without  the  use  of  individual 
lamps. 

The  next  scheme  was  a  selection  of  four  inverted  lamps  sup- 
ported from  the  ceiling  by  fixtures.     The  lamps  were  set  in 


4    i 

^     ± 

"co 
1—  1 

1 

.  (\  , 

-     . 

I 

Hh 

rih 

Elevation 


e 


C 
H 


Plan 

FIG.  42. — Plan  and  elevation  of  test  office  showing  second  trial  for 
improvement  of  lighting.  100-watt  (80  candle-power)  tungsten  lamps 
used. 

inverted  opaque  reflectors,  as  shown  in  Fig.  43,  while  the  ceiling 
served  as  a  reflecting  surface.  The  illumination  produced  by 
this  scheme  seemed  sufficient  at  night,  but  when  combined  with 
the  natural  light  during  the  day  was  entirely  inadequate  to 
illuminate  the  desks  properly  late  in  the  afternoon.  This  ex- 
periment indicated  the  necessity  for  more  artificial  light  during 


70 


FACTORY  LIGHTING 


the  day  than  at  night,  due  chiefly  to  the  effect  on  the  eye  of  the 
stimulus  from  ordinary  daylight.  The  pupil  is  in  a  contracted 
state  when  subjected  to  the  intensities  of  natural  light,  which 
makes  more  artificial  light  necessary  during  cloudy  days  to  give 
the  impression  of  satisfactory  illumination  than  when  the  eye 
is  under  the  influence  of  natural  darkness,  or  the  lower  intensities 


1 


Da. 


Plan 


FIG.  43. — Plan  and  elevation  of  test  office  showing  third  trial  for  im- 
provement of  the  lighting.  Total  and  semi-indirect  illumination  were 
given  trial. 

of  artificial  light  and  this  effect  seemed  more  noticeable  in  this 
trial  than  in  the  others. 

After  a  time  the  problem  of  maintaining  a  clean  ceiling  as  a 
reflecting  surface,  as  well  as  clean  inverted  reflectors,  appeared 
too  great  to  admit  of  this  system  in  this  particular  case.  It  may 
be  noted,  however,  that  the  energy  consumption  in  this  .trial  was 


OFFICE  LIGHTING 


71 


favorable,  and  all  eye  strain  resulting  from  direct  glare  practically 
removed.  The  tests  of  this  system  of  illumination  in  this 
particular  instance  were  not  satisfactory  for  the  conditions  of  the 
given  location,  but  it  should  not  be  inferred  that  such  a  scheme 
is  unsuitable  in  various  other  offices  where  the  conditions  may  be 
different. 


6 


Elevation 


-2'6#-  7'6- 

t.^..  -^es-.-^v 

i 

D 
C 

p 

^ 

C 

p 

C 

i 

|     n 

K 

H                « 

1 

A 

Plan 

FIG.  44. — Plan  and  elevation  of  test  office  showing  fourth  trial  and  final 
arrangement  of  lamps  for  improvement  of  the  lighting.  60-watt  (48  candle- 
power)  tungsten  lamps  and  Holophane  "Intensive"  type  reflectors  used. 

The  next  step  toward  the  improvement  of  the  lighting  condi- 
tions in  this  office  consisted  in  the  arrangement  of  nine  lamps  of 
comparatively  small  candle-power  equipped  with  suitable  re- 
flectors as  shown  in  Fig.  44.  In  this  case  the  various  lamps 
next  to  the  wall  were  moved  back  and  forth  until  their  location 
was  such  as  to  illuminate  properly  the  outside  desks,  and  it  was 


72  FACTORY  LIGHTING 

found,  after  securing  this  result  that  the  illumination  at  the  cen- 
tral portions  of  the  office  was  uniform  and  entirely  adequate. 
This  result  was  obtained  by  spacing  the  edge  rows  of  lamps  2  ft. 
6  in.  from  the  walls,  the  light  thus  being  satisfactory  for  all  wall 
desks  and  presenting  a  uniform  distribution  over  the  entire 
working  surface  of  the  room.  The  large  number  of  lamps 
permitted  the  use  of  a  small  candle-power  for  each  unit  and  thus 
obviated  the  eye  strain  found  in  the  previous  system  and  trials. 

It  should  be  noted  that  the  distance  from  the  edge  row  of 
lamps  to  the  wall  is  less  than  half  the  spacing  distance  between 
central  lamps,  and  the  arrangement  of  the  units  is  therefore  not 
entirely  symmetrical  with  respect  to  the  floor  space.  Ordinary 
rules  in  the  past  have  stated  that  edge  lamps  should  be  spaced  at 
a  distance  from  the  wall  equal  to  one-half  the  spacing  distance 
between  lamps,  but  in  general  this  scheme  will  be  found  unsatis- 
factory where  it  is  desired  to  illuminate  wall  desks  properly. 

The  spacing  distance  between  lamps  in  this  particular  case 
was  found  to  be  7  ft.  6  in.  this  spacing  being  required  in  order 
to  make  use  of  lamps  sufficiently  small  to  avoid  eye  strain.  It 
is  for  this  reason  that  a  spacing  of  approximately  7  ft.  6  in.  is 
considered  to  be  most  advantageous  for  average  office  lighting 
with  moderate  ceiling  heights,  and  it  is  recommended  that  in  no 
case  where  the  ceiling  height  is  12  ft.  or  under,  should  this 
spacing  distance  be  exceeded.  Under  some  limiting  conditions 
it  will  be  subsequently  described  how  a  smaller  spacing  distance 
is  sometimes  advisable,  and  also  that  for  higher  ceilings  the 
lamps  may  be  larger  and  spaced  farther  apart. 

51.  Simple  Rules. — These  and  numerous  experiments  in 
offices  of  different  sizes  and  heights  have  led  to  the  formulation 
of  certain  rules  which  may  be  applied  in  a  general  way  to  the 
satisfactory  illumination  of  practically  all  offices.  Caution, 
however,  should  be  given  regarding  the  use  of  such  rules  in  view 
of  the  fact  that  each  office  to  be  lighted  should  in  the  main  be 
taken  as  a  separate  problem  in  the  application  of  the  simple 
principles  just  outlined.  To  the  average  person,  the  necessity 
for  adherence  to  such  principles  is  not  apparent  on  account  of 
the  fact  that  differences  in  the  illumination  effects  resulting  from 
two  alternate  schemes  are  not  noticeable  unless  carefully 
studied  over  a  considerable  length  of  time,  and  yet  these  differ- 
ences and  the  application  of  set  rules  without  due  care  may  pro- 
duce results  which  are  quite  unsatisfactory  in  the  long  run. 


OFFICE  LIGHTING 


73 


T 


Elevation 
14'- 


The  following  may,  however,  be  taken  as  general  hints  for 
various  office-lighting  problems,  and  based  as  they  are  on  ex- 
tensive experiments,  they  will  be  found  to  afford  a  means  for  the 
betterment  of  unsatisfactory  conditions  in  many  cases,  or  for  the 
production  of  successful  results  in  those  locations  which  are 
about  to  be  equipped  with  lamps  for  the  first  time. 

(1)  Small  offices  occupied  by  a  single  person  or  by  a  single 
person  and  assistant,  should  be  treated  as  special  cases.     Usually 
one  lamp   mounted  high  over  the 

desk  will  be  satisfactory,  but  even 
here  four  or  six  lamps  at  the  ceiling 
are  often  far  more  satisfactory  than 
a  single  lamp  over  each  desk. 

(2)  Offices  up  to  14  ft.  on  a  side 
and  occupied  by  more   than  two 
persons,  require  general  illumina-  _1 
tion  from  over-head  lamps  of  suffi- 
cient intensity  to  eliminate  entirely 
the  necessity  for  individual   desk 
lamps.     Up  to  this  limiting  dimen- 
sion,  four   units  arranged  as  indi- 
cated in   Fig.   45  should  be  used 
with  the  edge  lamps  about  2  ft.  6 

in.  from  the  walls  to  take  care  of 
those  cases  where  the  desks  are 
located  against  and  facing  the  wall. 
It  will  be  noted  by  referring  to 
Fig.  45  that  the  spacing  distance 
of  7  ft.  6  in.  recommended  as  a 
maximum,  has  been  exceeded. 
This  is  due  to  the  awkward  dimen- 
sion of  the  office.  If  the  room  is  crowded  with  desks,  it  may  be 
well  to  class  the  14  ft.  office  under  the  following  heading,  that 
is,  equip  it  with  nine  lamps  and  use  the  smaller  spacing  thus 
called  for. 

(3)  Offices   with   dimensions   from    14   to   22   ft.    on  a   side 
should   be  equipped  with  nine  units  arranged  as  indicated  in 
Fig.  46,  and  the  edge  lamps  located  about  2  ft.  6  in.  from  the 
walls. 

(4)  Offices  with  dimensions  from  22  to  30  ft.  on  a  side  should 
be  equipped  with  16  lamps  arranged  in  a  symmetrical  manner  as 


xk 


* 


K 


H 


Plan 

FIG.  45. — Typical  office  equipped 
with  four  lamps  over  head. 


74  FACTORY  LIGHTING 

described  in  the  foregoing,  the  edge  lamps  to  be  about  2  ft.  6  in. 
from  the  walls. 

All  the  lamps  in  cases  of  this  kind  should  be  mounted  at  or 
near  the  ceiling  unless  the  ceilings  are  very  high.  If  the  ceilings 
are  16  to  20  ft.  high  the  lamps  should  be  mounted  lower,  say  11  or 
12  ft.  above  the  floor.  This  will  eliminate  glare  resulting  from 
the  direct  light  of  lamps  shining  into  the  eyes  of  those  working  in 
the  office.  Where  the  office  is  rectangular,  the  floor  space  may 
be  divided  into  elementary  squares  and  the  foregoing  rules 
applied.  Table  XI  will  be  found  useful  in  laying  out  the  illu- 
mination of  both  square  and  rectangular  offices.  The  values 
therein  given  indicate  the  number  of  rows  of  lamps  and  the 
number  of  lamps  per  row  required  for  offices  of  various  sizes  in 
order  to  fulfil  the  requirements  for  satisfactory  illumination. 
This  table  applies  primarily  to  offices  with  low  ceiling  heights 
up  to  about  12  ft.,  but  with  care  it  may  be  used  for  somewhat 
higher  ceilings  as  well. 

TABLE  XI. — SPACING   DISTANCES  SUGGESTED   FOE  OFFICE  LIGHTING 

WHERE  A  NUMBER  OF  PERSONS  OCCUPY  THE  SAME  OFFICE. 

OFFICES  OCCUPIED  BY  A  SINGLE  PERSON  MUST  BE  TREATED 

AS  SPECIAL  CASES.    THESE  VALUES  WERE  DERIVED  FROM 

THE  TEST  EXPLAINED  IN  CHAPTER  V 

When  the  ceilings  are  about  12  ft.  in  height 

Width  (or  length)  of  office.  Number  of  lamp  rows, 

Up  to  10  ft.  1  lamp  at  center 

10  to  14  ft.  2  rows. 

14  to  22  ft.  3  rows. 

22  to  30  ft.  4  rows. 

30  to  38  ft.  5  rows. 

38  to  46  ft.  6  rows. 

52.  Design  Factors. — As  shown  in  Art,  10,  Chapter  II,  the 
size  of  lamp  selected  for  various  office  conditions  involves  the 
question  of  glare  and  also  the  intensity  which  is  to  be  secured  in 
those  cases  where  the  spacing  has  been  determined  by  the  fore- 
going rules.  The  first  step  is  to  decide  on  the  spacing  of  the 
lamps  necessary  for  satisfactory  conditions  according  to  the 
experiments  just  mentioned.  The  size  of  the  lamp  should  then 
be  chosen  so  that  the  given  number  of  lamps  will  furnish  proper 
intensities  on  the  working  surface  as  described  in  Art.  17, 
Chapter  II. 

In  Art.  9,  Chapter  II,  the  choice  of  reflector  was  shown  to 
depend  upon  the  spacing  between  lamps  and  the  mounting 


OFFICE  LIGHTING 


75 


height  above  the  desk  surfaces,  while  the  reflecting  efficiency  of 
the  reflectors  will  largely  influence  the  resulting  illumination 
intensity  on  the  desks.  With  the  various  sizes  of  incandescent 
lamps  now  available  of  the  tungsten  type,  and  the  number  of 
reflectors  on  the  market,  it  is  nearly  always  possible  to  select  a 
combination  of  lamp  and  reflector  which  will  result  in  a  favorable 
efficiency  for  general  office  conditions. 


Elevation 
18- — 


(f«*H 6'  6— -^p 6'6— 

)$()$()$( 


H 


H 


K 


K 


Plan 
FIG.  46. — Typical  office  equipped  with  nine  lamps  over  head. 

A  Practical  Example. — Assuming  an  office  12  by  16  ft.  floor 
space,  Table  XI  shows  that  two  rows  of  lamps  with  three  lamps 
per  row  are  required  to  furnish  satisfactory  illumination.  Hav- 
ing selected  the  number  of  lamps,  six  in  all,  the  lamps  nearest 
the  walls  should  be  about  2  ft.  6  in.  from  the  walls  and  the  re- 
maining lamps  spaced  at  equal  distances  from  each  other.  The 
size  of  the  lamps,  type  of  reflector  and  the  remaining  items  to  be 
found  as  previously  explained. 


76  FACTORY  LIGHTING 

53.  High  Ceilings. — In  some  cases  the  ceiling  height  is  such 
that  the  lamps  may  be  mounted  higher  than  12  ft.     The  lamps 
are  then  well  above  the  line  of  vision  and  the  eye  strain  which  was 
the  cause  for  the  previously  described  experiments,  will  be  less 
even  with  larger  lamps  than  recommended  in  previous  paragraphs. 
It  may  be  practicable,  therefore,  to  use  a  smaller  number  of  lamps 
than  indicated  in  Table  XI,  so  that  each  lamp  may  be  larger  in 
candle-power.     Where  the  number  of  lamps  for  a  given  floor  may 
be  thus  reduced,  the  first  cost  of  the  initial  installation  is  some- 
what reduced,  and  with  a  little  study  beforehand  the  system  may 
be  made  to  meet  the  requirements  of  satisfactory  illumination. 

54.  Offices   of   Odd   Dimensions. — Table   XI   indicates  that 
with  certain  dimensions  there  may  be  a  choice  of  either  one  or 
another  number  of  lamp  rows.     An  office  14  ft.  wide,  for  example, 
may  be  equipped  with  either  two  or  three  rows  and  still  conform 
to  the  table.     In  like  manner,  an   office    22   ft.  wide  may  be 
equipped  with  either  three  or  four  rows. 

After  deciding  on  the  necessary  candle-power  and  the  equiva- 
lent energy  in  watts,  it  is  practically  immaterial  from  the  stand- 
point of  energy  consumption  alone  whether  this  energy  is  utilized 
in  the  form  of  one  large  lamp  or  many  small  lamps.  On  the  other 
hand,  the  first  cost  is  affected  by  the  number  of  lamps  on  account 
of  the  higher  cost  of  wiring  where  a  large  number  of  lamps  is 
used  for  a  given  area.  It  should  be  kept  clearly  in  mind,  how- 
ever, that  the  satisfaction  of  the  illumination  in  every  portion  of 
an  office  depends  almost  entirely  on  the  number  of  lamps  and  on 
the  manner  in  which  they  are  spaced.  The  use  of  a  larger  num- 
ber of  small  lamps  is  thus  generally  warranted  due  to  the  crowded 
condition  of  desks  in  many  offices,  although  for  the  particular 
case  of  semi-indirect  lighting  the  reflecting  character  of  walls 
and  ceiling  is  almost  as  large  a  factor  as  is  the  arrangement  of  the 
lamps. 

Fig.  47  shows  a  chart  giving  various  spacing  distances  of 
lamps,  as  well  as  the  spacing  distance  in  those  limiting  cases 
just  described.  This  chart  indicates  that  for  the  dimensions  of 
10,  14,  22  and  30  ft.,  there  is  a  choice  between  two  arrangements 
of  the  lamps.  This  chart  corresponds  with  Table  XI  and  is 
intended  merely  to  show  how  the  adherence  to  the  table  results 
in  certain  definite  lamp  arrangements. 

In  these  1'miting  cases  it  is  best  in  the  main  to  choose  the 
next  larger  number  of  lamp  rows  rather  than  to  use  the  smaller 


OFFICE  LIGHTING 


77 


number  for  the  sake  of  an  apparent  reduction  in  the  expense  with 
the  smaller  number.  This  stand  is  based  on  the  fact  that  the 
first  cost  for  lighting  equipment  is  an  item  which  must  be  consid- 
ered in  its  effect  on  the  work  of  the  office,  and  hence  is  a  charge 
which  should  be  spread  over  a  considerable  period  of  time.  In 
its  relation  to  the  satisfaction  of  those  using  the  office  the  first 
cost  of  the  lighting  should  be  given  secondary  place.  It  has 

Width  or  Length  of  Room 
8  Ft. 


One  Row  of  Lamps  j  |    4'o" 

tlO  Ft. 


4V 


5'0"     4-A       5'0" 


s'o 


4  Rows  x 


2  Rows-!  12  Ft. 

14  Ft. 
14  Ft. 
16  Ft. 
3  Rows  1  18  Ft.  p 

N 

20Ft.r7^ 
22  Ft. 
22  Ft. 
24  Ft.  p 
26  Ft.  r^-7. 
28  Ft. 
30Ft.p 

30  Ft. 

Etc. 


TO 


, 
12  e 


46 


s'e"  O*     sV 


ee 


66 


7 


76 


6 


ss 


58 


2  6 


70 


TO 


70 


78 


TS 


78 


O2'6'1 


84 


84 


84 


2'6%A 


63 


63 


es 


FIG.  47. — Spacing  of  lamps  suggested  for  offices  of  different  sizes,  where 
the  offices  contain  more  than  one  desk.  Offices  occupied  by  one  person 
only  should  be  treated  as  special  cases. 

been  found  again  and  again  that  the  first  cost  amounts  to  a  very 
small  percentage  of  the  wages  paid  the  employees.  In  one  case, 
for  example,  the  wages  for  about  two  minutes  per  day  were  equiva- 
lent to  the  entire  cost  of  lighting  for  that  day,  which  may  be 
intrepreted  to  mean  that  the  best  illumination  could  here  be 
reduced  to  the  equivalent  wages  for  a  two-minute  interval.  The 
first  cost_itself  is  likely  to  be  only  say  one- third  of  1  per  cent, 
of^the  wages  of  the  person  working  under  the  lamp  during  the 


78  FACTORY  LIGHTING 

several  years  it  is  assumed  to  be  used,  and  for  this  reason  why 
not  make  it  the  best  available?  Thus,  if  the  wiring  and  lamps 
cost  say  $5.00  per  person  in  an  office,  and  if  this  person  earns 
$500  per  year,  then  in  three  years  the  cost  for  the  lighting  is  but 
one-third  of  1  per  cent. 

It  is  apparent  that  the  losses  in  time  and  efficiency  due  to 
poor  light  may  be  classed  in  values  far  in  excess  of  such  a  small 
time  interval.  Hence,  if  there  is  a  choice  between  one  and  another 


T 


4        6        4 


1 


Elevation 


10 

1— I 

J 
ua 
i 


«rf  «  X  «  W 

«v»x  \«/  x~/ 

A  A  A 


i* 


Plan 
FIG.  48. — Office  15X35  feet  showing  typical  arrangement  of  lamps. 

system  in  which  either  a  large  or  a  small  number  of  lamps  is 
to  be  used,  it  should  be  remembered  that  if  what  may  be  termed 
the  inferior  system,  that  is,  the  one  with  the  smaller  number  of 
lamps,  results  in  a  loss  of  time  in  excess  of  two  minutes  per  day 
as  compared  to  the  superior  system,  the  smaller  number  of  lamps 
will  in  consequence  result  in  a  direct  loss  to  the  general  economy 
of  the  office  force. 

55.  Narrow  Office  15  by  35  ft.— Table  XI  and  Fig.  47  show 
that  three  rows  of  lamps  with  five  lamps  per  row  are  required. 
In  this  case  there  is  no  difficulty  in  a  selection  of  the  number 
of  lamps,  and  they  may  be  arranged  as  indicated  by  Fig.  48. 


OFFICE  LIGHTING 


79 


The  lamps  near  the  wall  should  be  about  2  ft.  6  in.  from  the  walls 
as  shown  in  the  diagram,  and  the  remaining  lamps  spaced  equi- 
distant from  each  other. 

56.  Small  Office  10  ft.  by  12  ft.  6  in.— Table  XI  and 
Fig.  47  show  that  either  one  or  two  rows  of  lamps  with  two  lamps 
in  each  row  may  be  selected.  Fig.  49  indicates  the  arrangement 
with  the  smaller  number,  and  Fig.  50  shows  the  larger  number 
of  lamps.  This  office  if  somewhat  too  wide  for  one  row  since  the 


6 


1 

4 

5 

1 

"o 

»H 

Elevation 

I- 12V 1 


Elevation 


f 


T 


¥ 


Plan  Plan 

FIG.  49.  FIG.  50. 

FIG.  49. — Lighting  arrangement  in  a  typical  office  10  X 12  ft.  6  in.  The 
10  ft.  dimension  gives  the  trouble  in  this  case.  One  row  of  lamps  may  be 
used  as  shown. 

FIG.  50. — Lighting  arrangement  in  a  typical  office  10X12  ft.  6  in.  where 
two  rows  instead  of  one  are  used.  The  10  ft.  dimension  gives  the  trouble 
in  this  case.  Compare  with  Fig.  49. 


desks  along  two  of  the  walls  are  not  properly  illuminated.  On 
the  other  hand,  the  office  is  almost  too  narrow  for  two  rows  since 
in  this  case  the  dimensions  along  the  narrow  side  of  the  office  be- 
tween lamps  is  but  5  ft.,  which  is  somewhat  smaller  than  is 
necessary  to  provide  sufficient  illumination  with  suitable  direc- 
tional features  for  all  the  desks. 

Again,  if  tungsten  lamps  are  to  be  used  here,  four  25-watt 
lamps  by  calculation  are  somewhat  too  small  and  four  40-watt 


80 


FACTORY  LIGHTING 


lamps  a  little  larger  than  necessary  for  adequate  illumination 
in  the  case  of  Fig.  50.  As  intermediate  sizes  of  lamps  are  not 
available,  and  as  a  lamp  too  small  for  the  requirements  should 
not  be  considered,  the  40-watt  lamp  is  the  only  alternative. 
If,  therefore,  the  larger  number  of  lamps  and  the  higher  candle- 
power  are  selected,  the  installation  will  possess  several  peculiar 
features.  The  office  will  appear  somewhat  over-lighted  because 


T 


j. 


Elevation 
20' 


H 


<jj 

1 


Plan 

FIG.  51. — Lighting  arrangement  in  a  typical  office  15X20  ft.  using  two 
rows  of  lamps  7  ft.  6  in.  apart.  The  15  ft.  dimension  gives  the  trouble. 
Note  that  the  desks  which  may  be  against  and  facing  the  walls  above  and 
below  will  not  be  properly  lighted.  The  lamps  are  too  far  from  these  two 
walls. 

the  lamps  are  spaced  closer  than  necessary,  and  furthermore 
the  lamps  being  larger  than  required  on  account  of  a  lack  of 
intermediate  sizes,  the  illumination  will  be  somewhat  excessive, 
both  in  the  number  of  lamps  and  in  the  resulting  intensity.  It 
will  be  noted  than  this  involves  two  distinct  considerations. 
The  larger  number  of  lamps  is  selected  to  produce  a  light  on 
the  desks  suitably  directed,  while  the  larger  size  is  selected  to 
produce  the  required  intensity.  It  is  strongly  recommended, 


OFFICE  LIGHTING 


81 


therefore,  in  limiting  cases  of  this  kind  that  the  larger  number  of 
lamps  with  the  higher  candle-power  be  selected. 

This  is  all  the  more  important  because  with  all  the  refinements 
in  securing  just  the  proper  intensity,  it  has  been  found  that  the 
average  performance  of  such  systems  is  considerably  below  the 
initial  values,  hence  the  initial  candle-power  of  the  lamps  and  the 
corresponding  intensity  on  the  desks  will  be  reduced  with  contin- 


•    £ 

H 

6                   6 

H 

, 

1 

Elevation 
«n                                .1 

h  •• 

iBU 

'    -2'6^^—  -1  ?'S-  *H  7'6-  H*26* 

vix       i                                            %-L/                                                     N-Lx 

(5--?—                           Q                                      Q 

X™\      A                                     X^\                                             /^N 

o 

H                               C 

r- 

> 

•« 

. 
j 

K                « 

g 

Plan 

FIG.  52. — Lighting  arrangement  in  a  typical  office  15X20  ft.,  using  two 
rows  of  lamps  2  ft.  6  in.  from  the  upper  and  lower  walls  in  the  figure.  These 
edge  lamps  furnish  adequate  light  to  desks  against  and  facing  these  two 
walls,  but  the  spacing  of  10  ft.  is  too  great  ordinarily.  Compare  with 
Fig.  51. 

ued  service  due,  first,  to  the  natural  deterioration  of  the  lamps, 
and,  second,  to  the  accumulation  of  dust  and  dirt  on  the  surfaces 
of  lamps  and  reflectors.  Hence,  what  may  at  first  appear  to 
be  a  rather  expensive  installation,  may  on  the  average  be  just 
satisfactory. 

57.  Rectangular  Office  15  by  20  ft.— Figs.  51,  52,  and  53 
show  another  limiting  case  where  from  the  table  and  chart  it  is 
found  that  the  office  is  somewhat  too  small  for  three  rows  and 


82 


FACTORY  LIGHTING 


somewhat  too  large  for  two  rows.  Two  rows  may  be  used  as 
shown  in  Fig.  51  and  the  recommended  spacing  of  7  ft.  6  in.  com- 
plied with,  but  here  the  lamps  are  too  far  from  two  of  the  walls 
to  produce  satisfactory  results  on  the  outside  wall  desks.  In  like 
manner,  two  rows  might  be  used  as  in  Fig.  52,  with  the  lamps 
properly  located  for  taking  care  of  wall  desks,  that  is,  2  ft.  6  in. 
from  the  walls,  but  with  the  result  that  the  interior  portion  of  the 


1  4 

6 

5 

H 

^ 

. 

Elevation 

i 

on' 

i 

ZU 

'    -2'6^-^ 

r'Q'l  ^_._7'6^ 

-.^.^g: 

&T 

k 

A 

lo 

3       »f 

» 

X 

la 

1 

)*t 
> 

X 

w 

Plan 

FIG.  53. — Lighting  arrangement  in  a  typical  office  15X20  ft.,  using 
three  rows  of  lamps  between  upper  and  lower  walls  in  the  figure.  This 
arrangement  is  superior  to  the  schemes  shown  in  Figs.  51  and  52,  but  may 
be  criticized  as  using  too  many  lamps  for  the  area  involved. 

office  where  the  spacing  is  10  ft.,  is  poorly  lighted.  In  Fig.  53, 
however,  an  arrangement  of  three  rows  is  shown  where  the  wall 
desks  as  well  as  those  at  the  central  portion  of  the  office  are  ade- 
quately lighted.  The  spacing  distance  between  lamps  along  the 
direction  of  the  narrow  portion  of  the  office  is,  however,  now  5 
ft.,  which  is  considerably  smaller  than  the  recommended  spacing 
of  7  ft.  6  in.  for  office  practice.  The  usual  safe  policy  in  a  case 
of  this  kind  should  be  to  lean  to  the  higher  number  of  lamps  for 
reasons  stated  in  a  previous  article. 


OFFICE  LIGHTING  83 

In  a  large  number  of  cases  possessing  these  limiting  conditions 
lamps  have  been  installed  with  the  higher  rather  than  the  lower 
number,  and  the  average  performance  has  indicated  that  the 
resulting  intensity  is  not  too  high  for  the  conditions  involved. 
Figs.  54  and  55  indicate  typical  offices  with  lamps  arranged 
according  to  the  rules  just  given.1 


FIG.  54. — Reproduced  from  a  photograph  taken  at  night  under  arti- 
ficial light  in  a  typical  office  lighted  according  to  the  suggestions  in  Chapter 
V.  60-watt  (48  candle-power)  tungsten  lamps  are  used  equipped  with 
Holophane  "Intensive"  type  reflectors. 

Indirect  and  Semi-indirect  Lighting. — Considerable  emphasis  in 
the  preceding  paragraphs  has  been  placed  on  the  arrangement  in 
offices  of  relatively  small  lamps.  Where  the  office  has  a  suitable 
ceiling,  that  is,  light  in  color,  a  smaller  number  of  outlets  with 
larger  lamps  so  arranged  as  to  send  much  of  the  light  to  the 
ceiling  and  thence  to  the  desks  by  reflection,  may  prove  as 
satisfactory  as  with  the  larger  number  of  lamps  furnishing  light 

^ee  articles  by  the  author  on  "Notes  on  Office  Lighting,"  Electric 
Journal,  VoL  VII,  pp.  352-358,  May,  1910;  and  on  "Lighting  of  Small 
Offices,"  Electric  Journal,  Vol.  VIII,  pp.  537-546,  June,  1911. 


84 


FACTORY  LIGHTING 


directly  to  the  desks  from  reflectors.  While  the  energy  required 
for  indirect  and  semi-indirect  lighting  is  often  higher  for  a  given 
intensity  than  where  direct  lighting  is  employed,  the  advantages 
gained  by  the  former  sometimes  entirely  offset  the  increased  cost 
for  energy  and  maintenance  if  these  items  happen  to  be  slightly 
higher  than  for  the  direct  system. 


FIG.  55. — Reproduced  from  a  photograph  taken  at  night  under  the  arti- 
ficial light  in  a  typical  office  lighted  according  to  the  suggestions  in  Chapter 
V.  60-watt  (48  candle-power)  tungsten  lamps  are  used  equipped  with 
Holophane  "Focusing"  type  reflectors. 


CHAPTER  VI 
DRAFTING-ROOM  LIGHTING 

58.  Difficult  Conditions. — Of  the  various  problems  in  indus- 
trial lighting,  that  of  the  drafting  room  is  difficult  in  a  peculiar 
manner.     The  constant  use  of  the  eye  in  the  distinction  of  fine 
lines  and  much  detail  requires  illumination  of  exceptional  qualities. 
In  addition  to  work  on  the  drawings,  various  instruments  and 
scales  must  continually  be  handled,  all  of  which  places  a  demand 
on  the  eye  equalled  in  but  few  other  classes  of  work. 

A  slight  shadow  is  often  noticeable  along  the  edge  of  ruling 
devices  as  with  the  triangle  and  the  T-square.  Shadows  are  also 
objectionable  when  handling  dividers,  bow-pens  and  other 
similar  instruments.  A  peculiar  feature  connected  with- the 
shadows  is  that  the  draftsman  in  an  effort  to  do  accurate  work 
often  overlooks  these  shadows,  but  the  constant  strain  thus 
produced  is  apt  to  result  in  early  fatigue  of  the  eyes  and  the  general 
physical  system,  to  a  considerably  greater  extent  than  if  the 
shadows  were  not  present.  The  shadows  depend  of  course  on 
the  direction  in  which  the  natural  or  artificial  light  reaches  the 
drawing. 

In  tracing,  the  light  must  be  sufficiently  intense  to  penetrate 
the  tracing  cloth,  and  in  practically  all  work  of  the  draftsman  the 
light  should  be  strong  enough  for  his  needs  and  yet  not  so  strong 
as  to  cause  a  blinding  or  partly  blinding  effect  from  the  drawing 
paper  or  from  instruments  on  the  table. 

59.  General  Requirements. — The  requirements  for  drafting- 
room  lighting  conform  in  a  general  way  to  those  of  other  forms  of 
industrial  lighting,  but  should  include  the  following  items  which 
differ  slightly  from  those  of  office  lighting: 

(1)  Sufficient  illumination  for  each  person  in  the   drafting 
room. 

(2)  An  arrangement  of  lamps  which  produces  a  satisfactory 
illumination   effect   without   regard   to   the   location   of   desks. 
This  is  a  requirement  specially  applicable  to  large  drafting  rooms, 
where  the  desks  may  be  shifted  now  and  then  due  to  changing 
conditions  in  the  conduct  of  the  work. 

85 


86  FACTORY  LIGHTING 

In  a  small  room  containing  one  or  two  drawing  boards  it  is  not 
particularly  difficult  to  have  a  lamp  located  directly  above  each 
desk  and  to  move  the  desk  lamp  in  case  it  is  found  necessary  to 
shift  the  desk,  but  in  a  large  number  of  factories  rearrangements 
of  desks  are  necessary  now  and  then  and  if  the  lamp  over  each 
desk  must  be  shifted  with  the  desk  the  expense  of  wiring  is  essen- 
tially increased. 

(3)  An  installation  of  lamps  which  will  avoid  eye  strain. 

(4)  A  type   of   lamp   and   an   arrangement  which  will    fur- 
nish illumination  on  the  drawing  boards  with  the  least  possible 
shadow  effect  in  the  use  of  instruments  and  ruling  devices. 

(5)  Illumination  with  an  intensity  which  permits  of  ready 
discernment  of  fine  lines  and  details,  and  sufficient  for  tracing 
work. 

60.  Eliminating  Shadows. — The  most  intense  shadow  is  cast 
by  an  object  that  intercepts  the  light  from  a  single  lamp.     A 
single  lamp,  however,  located  properly  with  respect  to  a  drawing 
board   can,   by   the  continual  changing  of  its  position,  be  made 
to  throw  the  light  in  a  direction  so  as  almost  entirely  to  prevent 
objectionable  shadows.     Where  there  are  two  drawing  boards, 
each  with  its  own  lamp,  and  where  the  light  from  one  lamp 
partly  illuminates  the  neighboring  board,  this  interaction  of  the 
light  complicates  the  problem,  and  this  complication  is  found  in 
many  drafting  offices  due  to  the  large  number  of  lamps  made 
necessary  by  crowded  desk  conditions. 

It  consumes  time  to  adjust  a  lamp  for  each  position  of  a 
triangle  or  T-square,  and  in  general,  lamps  close  to  the  work  not 
only  require  a  certain  amount  of  time  in  such  adjustment,  but 
are  also  to  some  extent  in  the  way  of  the  draftsman  in  the 
performance  of  his  work.  An  engineering  investigation  con- 
ducted to  ascertain  the  best  means  for  securing  convenience  and 
avoiding  shadows  in  these  cases  has,  through  a  number  of  ex- 
periments, shown  that  probably  the  best  method  for  illuminating 
the  desk  surfaces  in  the  drafting  room  is  by  means  of  over-head 
lamps  arranged  for  the  elimination  of  shadows. 

61.  A   Practical   Investigation. — For    the  purpose  of  finding 
some  standard  scheme  for  lighting  the  drafting  room,  an  investi- 
gation covering  a  considerable  length  of  time  was  undertaken 
somewhat  as  follows: 

A  given  bay  in  a  large  room  was  taken  as  the  basis  for  the 
study.  The  size  of  the  bay  was  16  by  20  ft.  and  the  ceiling 


DRAFTING-ROOM  LIGHTING 


87 


height  11  ft.  6  in.  This  bay  contained  a  number  of  lamps 
approximately  as  shown  in  Fig.  56,  the  size  of  the  lamps  being 
rather  large  and  the  mounting  height  relatively  low.  The 
arrangement  of  lamps  was  equivalent  to  2.5  watts  per  square 
foot.  The  original  scheme  for  lighting  in  this  room  is  a  good 
illustration  of  the  interaction  between  a  number  of  large  lamps 
in  producing  shadows,  because  quite  a  number  of  the  lamps 
contribute  to  the  illumination  of  a  single  desk. 


Elevation 
20' — 


- —  5 


-co 10 


Plan 

FIG.  56. — Plan  and  elevation  of  bay  in  a  typical  drafting  room  showing 
original  lighting  arrangement.  300  candle-power  lamps  were  used,  shadows 
were  intense,  and  the  glare  very  objectionable. 


This  scheme  was  the  source  of  numerous  complaints,  and  the 
objectionable  features  may  be  enumerated  as  follows: 

(1)  The  illumination  was  poorly   distributed,   that  is,  some 
desks  received  a  higher  intensity  of  illumination  than  others. 

(2)  The  lamps  being  mounted  fairly  close  to  the  desks  resulted 
in  glare  which  was  disagreeable  and  harmful  to  those  persons 
who  in  certain  positions  received  the  direct  light  from  the  large 


88 


FACTORY  LIGHTING 


lamps  whenever  looking  up  from  their  work,  and  who  were  also 
subject  to  the  glare  from  papers  and  instruments. 

(3)  The  shadows  cast  by  the  relatively  small  number  of  large 
lamps  were  dense,  and  required  a  constant  shifting  of  ruling 
devices  so  that  the  light  might  be  received  on  the  work  at 
the  proper  angles,  and  this  task  was  difficult  even  with  shifting 
the  work  because  of  the  trouble  to  get  the  light  from  suitable 
directions. 


I 


N 

1 


£  4 


Elevation 
20' 


T 


i. 


** 


-  —    6- 


- 


XX 


a 


'H 


Plan 


FIG.  57.  —  Plan  and  elevation  of  bay  in  typical  drafting  room  showing 
first  trial  for  improvement  of  the  lighting.  100-watt  (80  candle-power) 
tungsten  lamps  were  used. 

After  an  analysis  of  the  conditions  which  were  the  cause  of 
the  complaints,  the  work  of  solving  the  difficulties  was  under- 
taken in  a  systematic  manner  and  at  the  outset  an  endeavor  was 
made  to  secure  the  five  requirements  for  good  drafting-  room 
lighting  as  stated  in  a  previous  paragraph. 

As  a  first  step,  nine  lamps  somewhat  smaller  in  size  than 
originally  used  were  installed  in  a  single  bay  as  shown  in  Fig.  57. 
This  sample  installation  resulted  in  a  sufficiently  intense  light 


DRAFTING-ROOM  LIGHTING 


89 


and  was  more  uniform  than  the  original  system  with  less  glare. 
It  will  be  noted,  however,  that  the  shadows  cast  by  the  larger 
number  of  relatively  small  lamps  were  nine  per  bay  instead  of 
four  as  formerly,  and  while  each  shadow  was  somewhat  less 
intense  because  offset  to  some  extent  by  the  light  of  neighboring 
lamps,  the  excessive  shadows  were  found  to  be  a  decided  objec- 
tion. When  drawing  a  circle  with  a  bow-pen,  nine  shadows 


T 

i 

V-i 

T 
I 

T 


Elevation 
20- 


1 


10' 4- —  5  - 


»x*f 


Plan 


FIG.  58. — Plan  and  elevation  of  bay  in  typical  drafting  room  showing 
second  trial  for  improvement  of  the  lighting.  The  larger  lamps  are  100- 
watt  (80  candle-power)  and  the  smaller  40-watt  (32  candle-power)  tungsten 
lamps,  grouped  as  indicated. 


stood  out  in  all  directions  from  the  instrument  and  rotated  with 
relative  motion  when  a  circle  was  described,  thus  adding  a  con- 
fusing and  annoying  element.  Considerable  complaint  resulted 
from  this  first  trial. 

It  was  then  suggested  that  a  still  larger  number  of  lamps 
per  bay  might  reduce  the  shadow  effect,  particularly  if  the  lamps 
were  arranged  in  groups  instead  of  being  installed  as  single  units. 


90  FACTORY  LIGHTING 

As  a  second  step,  therefore,  twelve  units  arranged  in  groups  were 
placed  in  service  as  shown  in  Fig.  58,  the  system  being  made  up 
of  four  groups,  each  containing  one  100-watt  and  two  40-watt 
tungsten  lamps.  Draftsmen  who  worked  under  this  scheme  for 
some  days  soon  experienced  the  same  trouble  as  before  from 
shadows,  and  the  effect  was  even  more  noticeable  on  account  of 
the  four  groups  of  lamps  in  a  single  bay  instead  of  nine  single 
units.  It  will  also  be  noted  that  although  the  number  of  lamps 
per  bay  was  larger  in  this  trial,  the  uniformity  of  the  light  was 
less  satisfactory  than  with  nine  distributed  lamps.  The  single 
group  of  lamps  in  the  last  scheme  served  to  take  the  place  of  a 
single  unit  in  the  first  trial  in  its  relation  to  the  illumination 
distribution  over  the  desks.  The  last  scheme  did  not,  therefore, 
conform  in  a  satisfactory  manner  to  the  needs  of  the  case. 

The  next  step  was  the  extreme  use  of  twenty-one  lamps  in  a 
single  bay,  the  idea  here  being  to  have  the  entire  ceiling  a  mass 
of  light  in  the  hope  of  eliminating  the  shadows.  The  effect  was 
somewhat  novel  in  that  the  bay  appeared  intensely  and  very 
brightly  lighted.  The  shadows  seemed  somewhat  offset  by  the 
high  intensity,  that  is,  the  eye  did  not  respond  to  the  spaces 
which  were  ordinarily  in  shadow,  but  the  idea  of  using  such  a 
scheme  was  entirely  out  of  the  question  on  account  of  the  expense 
of  lamps  in  such  numbers  for  a  given  floor  area. 

A  fourth  scheme  was  the  installation  of  four  250-watt  tungsten 
lamps  per  bay,  each  lamp  being  equipped  with  a  broadly  distribut- 
ing reflector.  It  was  suggested  that  the  high  intensities  of  light 
at  small  angles  below  the  horizontal  might  be  such  as  to  build  up 
the  intensity  at  various  points  on  the  drawing  boards  where 
shadows  previously  existed.  Under  good  conditions  where 
there  are  no  obstacles  as  is  the  case  with  drawing  boards  rather 
than  machinery,  the  illumination  in  this  scheme  might,  under 
favorable  circumstances,  be  built  up  at  given  points  otherwise  in 
shadow,  by  the  light  from  lamps  at  some  distance  from  the  worker. 
This  theoretical  consideration,  however,  is  offset  to  some  extent 
by  practical  conditions  in  the  average  drafting  room,  and  also 
by  the  fact  that  lamps  of  this  high  candle-power  are  too  large  for 
relatively  low  ceilings.  The  engineering  features  of  the  building 
up  of  the  light  from  lamps  with  broadly  distributing  reflectors 
is  at  least  interesting  even  if  of  no  particular  help  in  this  case. 

A  fifth  scheme,  and  the  one  finally  chosen,  was  based  on  the 
principle  that  light  furnished  from  a  source  of  large  area  practi- 


DRAFTING-ROOM  LIGHTING 


91 


cally  eliminates  shadows.  It  is  possible  to  secure  a  very  large 
area  of  light  source  where  individual  lamps  are  mounted  so  as  to 
throw  their  light  directly  upon  the  work  in  case  of  the  tungsten 
type  only  where  the  lamp  is  surrounded  by  a  large  globe,  and 
even  this  is  limited.  By  inverting  the  lamps,  however,  and  using 
a  reflector  which  not  only  transmits  but  diffuses  some  of  the  light 
from  the  lamp  the  area  of  light  source  is  increased,  and  this  is  still 
further  increased  if  the  lamps  are  mounted  in  the  inverted  position 
close  enough  to  the  ceiling  to  permit  the  reflection  from  the  ceiling 
of  whatever  light  reaches  it. 


FIG.  59. — Four-lamp  fixture  designed  for  drafting  room  lighting.     60-watt 
(48  candle-power)  tungsten  lamps  and  "Alba"  glass  reflectors  are  used. 

In  the  chosen  arrangement,  a  trial  of  opaque  reflectors  was 
made.  Here  no  light  is  transmitted  directly  to  the  work  but 
the  ceiling  is  used  to  reflect  the  bulk  of  the  light  to  the  work. 
This  scheme  while  providing  practically  uniform  and  shadowless 
illumination,  did  not  seem  adequate  unless  rather  large  lamps 
were  used.  Various  methods  of  mounting  the  lamps  for  the 
inverted  arrangement  were  given  trial,  one  of  which  was  the  use 
of  a  three  light  fixture  with  the  lamps  in  a  vertical  position  and 
also  when  in  an  angular  position  directed  toward  the  ceiling 
but  somewhat  away  from  the  fixture.  Later  a  four-light  fixture 


92 


FACTORY  LIGHTING 


as  shown  in  Fig.  59  was  tried,  and  with  reflectors  capable  of 
diffusing  the  light  and  which  at  the  same  time  directed  some  of 
the  light  to  the  ceiling,  this  scheme  seemed  to  fulfil  the  various 
requirements. 

62.  Combined  Direct  and  Indirect  Light.  —  The  foregoing 
investigation  with  the  accompanying  results  shows  some  of  the 
refinements  of  the  principles  of  illumination  which  may  be 
utilized  in  securing  definite  results.  The  method  finally  chosen 
makes  use  of  direct  light  in  as  far  as  the  reflectors  transmit  a 
certain  part  of  the  light  directly  to  the  drawing  boards,  and  of 


1 

|H     H     K 

H       H 

s     s     s 

1 

is     K     s 

^K       K 

^ 

|  -3-4-8-'  8- 

5  $  VY 

^    ^        (T-S 

4w       W       w 

t  /^N                      /""N                      S**\ 

K8  S  «8 

«\i/          V.LX 
M           M 

1  w 

|s     s     « 

Column 
)-(            )-( 

n      H      ^ 

J 

wte     s     s 

)-(            )-( 

K       K       K 

^^ 

>'4-- 


FIG.  60. — Plan  of  typical  drafting  room  showing  fifth  trial  and  final  ar- 
rangement for  improvement  of  the  lighting.  Note  spacing  as  compared  to 
Figs.  5Q,  57  and  58.  Each  outlet  shown  in  this  diagram  is  equipped  with  a 
four-lamp  fixture  as  shown  in  Fig.  59. 

indirect  light  as  regards  that  part  of  the  light  which  is  trans- 
mitted to  the  ceiling  and  in  turn  reflected  to  the  boards.  The 
reflectors  best  adapted  to  this  work  were  not  chosen  primarily 
for  their  reflecting  efficiency,  but  for  the  diffusion  quality  pre- 
viously mentioned.  A  reflector  of  the  Alba  type1  gave  an  ex- 
cellent result.  In  Fig.  60  the  general  arrangement  of  fixtures  is 
shown,  which  produces  illumination  at  once  uniform,  free  from 
objectionable  glare,  and  softened  by  the  quality  of  the  glass  which 
gives  the  light  a  pleasing  yellow  tone. 
1  Manufactured  by  the  Macbeth-Evans  Glass  Company  of  Pittsburgh. 


DRAFTING-ROOM  LIGHTING  93 

Shadows  were  almost  entirely  eliminated  and  by  the  choice  of 
a  suitable  size  of  lamp,  the  intensity  was  made  adequate  through- 
out the  room.  Considerable  emphasis  must  be  placed  on  the 
spacing  distance  between  fixtures  and  the  distance  from  lamps  to 
the  ceiling,  also  the  distance  from  the  floor  to  ceiling.  Various 
installations  of  drafting-room  lighting  have  been  made,  based 
on  the  foregoing  investigation,  some  of  which  have  been  entirely 
successful,  but  in  some  cases  where  the  spacing  has  been  changed 
from  that  originally  found  desirable,  the  shadows  have  been 
somewhat  increased.  Thus  with  a  slightly  larger  spacing  dis- 
tance than  that  shown  in  the  illustration,  the  shadow  effect 
has  been  found  large  enough  to  make  the  illumination  rather 
unsatisfactory. 

A  number  of  experiments  were  made  by  raising  and  lowering 
the  fixtures  in  order  to  determine  the  relation  between  the  direct 
light  from  the  reflector  and  the  reflected  rays  from  the  ceiling. 
The  distance  of  2  ft.  6  in.  between  lamps  and  ceiling  seemed  to 
furnish  the  best  relation,  that  is,  the  net  efficiency  of  the  two 
components  seemed  greatest  with  this  mounting  condition. 

63.  Illumination  Features. — The  average  intensity  for  draft- 
ing work  may  be  placed  at  7  foot-candles.  Higher  intensities  are 
recorded,  even  up  to  10  foot-candles,  and  lower  values  down  to 
5  foot-candles,  although  much  deviation  from  the  average  given 
is  apt  to  produce  poor  results. 

With  the  combination  of  direct  and  indirect  lighting  as  just 
explained,  and  where  the  ceiling  and  wall  conditions  are  such  as 
to  aid  the  lamps  by  their  light-colored  surfaces,  an  average  of 
three  watts  per  square  foot  for  tungsten  lamps  rated  at  1.25  watts 
per  candle,  produces  a  satisfactory  result.  This  value  of  watts 
per  square  foot  is  practically  the  same  as  was  the  case  in  the 
original  installation  where  the  foregoing  experiments  were  made, 
but  the  illumination  is  so  much  superior  with  the  new  arrange- 
ment that  there  is  no  comparison  between  the  illumination  of 
the  two  extremes.  It  should  be  remembered  that  as  the  rating 
of  tungsten  lamps  changes  these  values  of  watts  per  square  foot 
likewise  change. 

The  installation  expense  of  fixtures  for  inverted  lamps  is 
slightly  higher  than  for  a  system  of  direct  lighting.  When, 
however,  consideration  is  given  to  the  small  percentage  of  the 
labor  cost  of  the  average  drafting  room  which  is  equivalent  to 
the  cost  for  artificial  lighting,  the  difference  between  one  and 


94  FACTORY  LIGHTING : 

another  scheme  of  lighting  is  small  indeed,  as  far  as  the  resulting 
advantages  to  the  draftsmen  from  the  superior  illumination  are 
concerned. 

It  is  interesting  when  drafting  rooms  are  presented  for  light- 
ing equipment,  to  ascertain  the  total  wages  per  day  in  the  entire 
room  and  to  equate  the  entire  cost  of  lighting  per  day  in  the  room 
to  the  wages  for  the  number  of  minutes  which  are  equivalent  to 
the  lighting  cost.  It  may  be  found,  for  example,  that  in  a  large 
drafting  room  the  inverted  system  of  tungsten  lamps  can  be  paid 
for  by  the  wages  of  five  or  six  minutes  per  day.  It  is  rather 
surprising  to  compare  this  cost  relation  with  the  similar  relation 
between  the  wages  and  the  cost  of  an  inferior  lighting  system, 
which  may  be  found  to  equal  the  wages  of  four  or  five  minutes 
per  day.  The  difference  therefore  between  a  good  and  a  poor 
lighting  system  often  amounts  thus  to  but  one  or  two  minutes 
per  day.  Considerations  of  this  kind  are  most  convincing  in 
establishing  the  warrant  for  the  superior  arrangement  of  lamps. 
In  short,  if  the  better  scheme  insures  a  net  saving  of  but  one  or 
two  minutes  per  day  by  increasing  the  facilities  for  superior  and 
more  rapid  work,  there  is  no  economy  whatever,  but  an  actual 
loss  to  the  efficiency  of  the  entire  drafting  room,  by  using  the 
inferior  system  because  it  may  be  a  little  cheaper.  In  a  certain 
case  when  two  rooms  were  in  use,  one  with  individual  units  and 
the  other  with  the  semi-indirect  lighting,  the  chief  said  he  would 
prefer  men  to  work  seven  hours  per  day  with  the  good  lighting 
than  seven  and  one- half  hours  with  the  light  from  individual 
lamps. 

64.  Various  Fixture  Combinations. — It  has  been  found  that 
four  units  per  fixture,  although  selected  somewhat  at  random  at 
the  outset,  have,  after  a  trial  of  other  schemes,  seemed  best 
suited  to  this  class  of  work.  Formerly  a  single  large  unit  had 
been  tried  in  the  place  of  the  four-lamp  arrangement,  the  single 
unit  being  enclosed  by  a  large  reflector.  Apparently  the  single 
unit  somewhat  reduces  the  advantage  gained  by  the  large  area 
from  the  four- unit  scheme,  and  although  one  larger  lamp  at  each 
outlet  may  appeal  somewhat  from  the  standpoint  of  appearance, 
the  shadow  effect  seems  to  be  greater  than  in  the  case  of  the  four 
units  per  fixture.  Various  devices  are  on  the  market  for  securing 
or  approximately  securing  the  results  of  this  combination  of  direct 
and  indirect  lighting,  but  for  average  factory  drafting  conditions 
the  fixture  shown  in  Fig.  59  can  readily  be  made  up  of  ordinary 


DRAFTING-ROOM  LIGHTING 


95 


conduit  and  elbows,  with  a  reducer  at  the  point  where  the  socket 
is  attached  to  the  fixture.  Such  improvised  fixtures  are  relatively 
inexpensive  and  serve  every  purpose  as  far  as  excellence  of  the 
illumination  is  concerned,  although  there  is  a  great  variety  of 
fixtures  available  on  the  market  from  which'  a  selection  may  be 
made  to  suit  practically  any  case. 

65.  Other  Conditions. — Some  cases  are  apt  to  arise  where 
there  is  no  ceiling  from  which  to  derive  the  advantages  of  ceiling 
reflection.  Fig.  61  shows  a  scheme  that  has  been  devised  to 
take  care  of  such  conditions.  The  plates  supported  directly 
above  the  lamps  serve  the  purpose  of  a  ceiling.  This  plan  is 
fairly  simple  and  may  be  installed  where  the  requirements  of 


Reflecting 

surface,  which  can  be  folded 
during  the  day,  preventing  any 
obstruction  to  the  daylight. 


FIG.  61. — Plates  designed  as  substitute  for  ceiling  thus  making  possible 
semi-indirect  lighting  over  the  drawing  tables  beneath. 

the  work  seem  to  warrant  the  expense  thus  incurred  for  securing 
the  results  of  the  inverted  or  semi-indirect  arrangement.  Fig. 
62  is  reproduced  from  a  photograph  of  such  an  installation  and 
shows  the  lamps  mounted  directly  below  the  iron  plates,  these 
plates  taking  the  place  of  the  ceiling  in  the  office  shown.1 

Attention  should  be  given  the  choice  of  reflector  for  this 
method  of  lighting  and  the  bowl  shape  as  shown  in  the  illustration 
is  preferable  to  a  flat  type  with  which  a  portion  of  the  lamp  is 
exposed  when  the  fixtures  are  viewed  at  some  distance.  Further, 
the  efficiency  of  the  reflector  is  not  the  largest  item,  because 
what  is  desirable  is  that  quite  a  proportion  of  the  light  be  trans- 
mitted through  the  glass.  For  this  reason  the  prismatic  glass, 
although  more  efficient,  does  not  seem  so  well  adapted  for 
inverted  use  as  a  reflector  of  the  opalescent  type. 

1  See  article  by  the  Author  on  "Drafting  Room  Lighting  Problems," 
American  Machinist,  Vol.  XXXIV,  pp.  686-689,  April  13,  1911. 


96  FACTORY  LIGHTING 

It  is  essential  also  to  have  the  ceiling  and  the  upper  part  of 
walls  fairly  light,  and  the  retinting  of  the  walls  and  ceiling  from 
time  to  time  is  an  actual  economy  in  the  maintaining  of  illumina- 
tion facilities  through  the  medium  of  the  inverted  lamps. 

The  principles  just  enumerated  are  found  to  apply  in  a  number 
of  cases  other  than  drafting  rooms,  as,  for  example,  in  the  com- 
posing rooms  of  printing  houses.  Type  forms,  when  resting  on 
horizontal  table  surfaces,  must  be  read  with  the  eye  of  the  ob- 


FIG.  62. — Reproduced  from  a  photograph  taken  at  night  under  the  arti- 
ficial light  in  a  drafting  room  equipped  with  a  substitute  ceiling  as  shown 
in  Fig.  61.  100-watt  (80  candle-power)  tungsten  lamps  and  "Alba"  glass 
reflectors  are  used. 


server  fairly  close  to  the  type.  It  has  been  suggested  that 
shadowless  illumination  in  such  cases  will  be  somewhat  of  an 
objection  due  to  an  absence  of  relief  on  the  edges  of  the  type. 
From  observation  it  has  seemed  that  the  minute  shadows 
evident  even  with  the  inverted  system,  are  sufficient  to  give  the 
needed  relief  to  the  type,  and  it  is  quite  possible  that  a  very  small 
shadow  effect,  which  is  practically  not  noticeable  in  this  system, 
may  in  reality  be  an  advantage  in  a  case  of  this  kind. 


DRAFTING-ROOM  LIGHTING 


97 


As  shown  in  the  various  diagrams,  an  average  spacing  distance 
of  no  more  than  8  to  10  ft.  is  necessary  with  average  ceiling 
heights  from  12  to  16  ft.  in  large  drafting  rooms,  in  order  to  secure 
the  best  results  with  the  four-light  fixture.  These  fixtures  may 
then  be  equipped  with  60- watt  tungsten  lamps,  enclosed  in  some 
type  of  opalescent  bowl- shaped  reflector  as  shown  in  Fig.  63,  and 
the  result  will  in  most  cases  be  found  to  justify  the  care  and  ex- 
pense connected  with  the  trial  and  installation  of  the  system. 


FIG.  63. — Reproduced  from  a  photograph  taken  at  night  under  the 
artificial  light  in  a  drafting  room  equipped  with  four-light  fixtures  as  shown 
in  Figs.  59  and  60. 


While  much  has  been  said  regarding  the  advantages  of  the 
inverted  or  semi-indirect  tungsten  lighting  scheme  for  the  draft- 
ing room,  it  should  be  noted  that  the  mercury  vapor  lamp  pos- 
sesses many  points  favorable  for  this  purpose.  The  length  of  the 
tube,  which  is  the  light  source,  is  such  as  to  greatly  reduce  shad- 
ows, and  in  many  instances  this  type  of  lamp  is  in  service  for 
drafting  work  with  excellent  results. 


CHAPTER  VII 
FACTORY  LIGHTING 

66.  New  Ideas  Regarding  Factory  Conditions. — A  marked 
change  has  become  evident  toward  factory  environment  during 
recent  years.  This  change  in  attitude  has  resulted  in  a  great  deal 
of  attention  to  the  improvement  of  such  items  as  that  of  factory 
lighting.  The  basis  for  this  change  in  attitude  as  regards  light- 
ing may  be  included  under  the  following  heads: 

Economic  Relations. — Factory  managers  have  come  to  realize 
the  importance  of  suitable  surroundings  in  their  relation  to  sat- 
isfied workmen  and  to  greater  output.  The  old  ideas  of  having 
the  work  done  without  regard  to  surroundings  has  given  way 
to  a  study  of  environment  in  its  relation  to  improved  efficiency 
in  shop  operations.  Adequate  light  increases  output  and  it 
has  been  found  that  a  saving  of  four  or  five  minutes  per  day  for 
the  average  workman  actually  pays  for  the  entire  cost  of  operat- 
ing a  modern  equipment  of  factory  lighting.  This  relation  is 
shown  in  Fig.  64.  There  are  other  features  which  promote 
efficiency  in  the  plant  such  as  adequate  ventilation,  an  efficient 
heating  system,  the  maintaining  of  cleanliness  and  neatness, 
and  other  items  all  of  which  have  an  indirect  influence  on  the  out- 
put and  which  improve  the  living  conditions  in  the  factory. 

In  early  morning  and  late  afternoon  hours  and  on  the 
cloudy  days  throughout  the  year,  many  factory  locations  are 
in  practical  darkness  as  far  as  natural  light  is  concerned.  A 
good  system  of  artificial  light  aids  production  at  these  times  and 
thus  tends  to  maintain  efficient  workmanship  throughout  the  work- 
ing day.  In  like  manner,  the  night  turn  in  many  shops  must 
depend  altogether  on  artificial  light  so  that  lighting  as  an  eco- 
nomic factor  is  here  apparent.  The  importance  of  factory 
lighting  can  thus  scarcely  be  overestimated  and  attention  to 
those  items  which  affect  the  excellence  of  the  light  is  of  much 
weight  both  as  regards  the  economy  of  the  plant  and  the  comfort 
of  the  employee. 

New  Lamps  Available. — A  decade  ago  factory  lighting  was 
practically  limited  to  the  carbon  filament  lamp  on  the  one  hand, 

98 


FACTORY  LIGHTING 


99 


Energy  at  1  Cent 
per  Kilowatt-Hour 


10  Men 

1000  Square  Ft. 
Tungsten  Lighting 
Watts  per  Sq.  Ft.  Assumed 


..amps  Burning  5  Hours  per  Day 


All  Lamps  Burning  4  HOUTS  per  Day~ 


All  Lamps  Burning  3  Hours  per  Da 


All  Lamps  Burning  2  Hours  per  Day 


All  Lamps  Burning  1  Hours  per  Day 


34567 
Working  Periods  in  Minutes 


Energy  at  2  Cents 
per  Kilowatt-Hour 


Lamps  Burning  2  Hours  per  Day 


Lamps  Burning  1  Hours 


45678 
Working  Periods  in  Minutes 


Energy  at  3  Cen 
per  Kilowatt-Hour 


All|  Lamps  Burning  2  Hours  per  Day 


Lamps  Burning  1  Hours  per  Day 


FIG.  64. — Diagram  showing  relation  of  average  wages  to  lighting  costs. 


100  FACTORY  LIGHTING 

and  the  arc  lamp  on  the  other.  Both  of  these  types  are  still 
used  but  numerous  cases  arise  in  almost  every  factory  which 
come  under  the  head  of  intermediate  conditions.  These  inter- 
mediate locations  are  made  up  of  floor  areas  with  ceiling  heights 
ranging  from  12  to  18  ft. 

With  these  moderate  ceiling  heights  the  carbon  filament 
lamp  cannot  be  used  economically  unless  placed  close  to  the  work 
or  possibly  in  clusters  near  the  ceiling.  Both  of  these  schemes 
are  expensive  in  maintenance  and  energy  consumption,  as  well 
as  unsatisfactory  from  the  illumination  standpoint.  Arc  lamps 
in  these  cases  require  a  considerable  separation  and  on  this 
account  provide  a  poor  distribution  of  the  light  and  to  some  extent 
are  in  the  line  of  vision  which  causes  glare. 

As  explained  in  a  former  chapter,  the  introduction  of  the 
new  types  of  lamps  with  candle-power  values  intermediate 
between  those  of  the  carbon  filament  and  the  arc  lamp,  has  made 
possible  the  solution  of  many  problems  related  to  these  inter- 
mediate conditions  in  a  way  not  possible  by  either  of  the  older 
types.  A  brief  review  of  the  influence  of  these  new  types  of 
lamps  shows  that  a  new  era  in  factory  lighting  has  been  reached, 
and  an  important  feature  of  this  new  era  is  the  scientific  planning 
and  installing  of  lamps  in  a  manner  which  adapts  the  most 
economic  size  of  lamp  to  each  location  and  class  of  work,  and  the 
giving  of  due  weight  to  the  indirect  gains  x>f  good  light  all  of 
which  piomote  a  better  as  well  as  a  larger  output. 

Popular  Ideas. — Numerous  articles  dealing  with  popular 
opinion  regarding  the  subject  of  factory  environment  have 
referred  to  lighting  as  well  as  other  conditions  throughout  the 
country.  This  indicates  a  growing  attention  of  the  public 
to  these  conditions  and  shows  that  the  American  people  is  becom- 
ing alive  to  the  necessity  for  improved  factory  surroundings. 
This  popular  interest  has  resulted  in  legislative  measures  in 
some  of  the  states  where  certain  standards  of  environment 
have  been  adopted,  and  it  is  also  of  interest  to  note  that  in  a 
recent  message  to  Congress  a  President  of  the  United  States 
called  attention  to  the  surroundings  in  the  government  build- 
ings throughout  the  United  States. 

It  is  believed,  however,  that  one  of  the  strongest  features 
as  far  as  the  factory  owner  is  concerned,  is  the  economic  rela- 
tions of  improved  factory  conditions  to  the  production  and  gen- 
eral workmanship,  and  for  this  reason  greater  emphasis  is  placed 


FACTORY  LIGHTING  rl6l 

on  the  economic  side  of  the  subject  than  on  the  popular  or  legis- 
lative side,  in  the  subsequent  pages. 

67.  Various  Items  Concerning  the  Work  and  Surroundings. — 
It  is  not  the  intention  to  attempt  a  classification  of  factory 
work  to  cover  all  cases,  the  diversity  of  buildings  and  classes 
of  work  making  this  impracticable.  Some  of  the  important 
items  as  related  to  the  artificial  light  will,  however,  be  discussed 
in  the  following  paragraphs. 

Ceiling  Height. — From  the  viewpoint  of  the  lighting,  one  of 
the  most  satisfactory  divisions  of  factory  buildings- is  under  the 
head  of  ceiling  height  or  the  mounting  height  of  lamps  which 
is  possible  under  given  conditions.  As  previously  explained,  the 
size  of  the  lamp  and  the  spacing  depend  on  this  height,  and 
for  this  reason  the  various  locations  naturally  group  themselves 
into  spaces  with  varying  ceiling  heights. 

Nature  of  Factory  Work. — The  various  factory  operations  com- 
monly found  may  be  divided  into  two  main  groups  as  regards  the 
illumination  required.  First,  those  cases  where  the  work  is 
mostly  on  horizontal  surfaces,  as  in  bench  work  of  some  kinds  and 
in  some  assembly  work,  where  practically  only  downward  illumi- 
nation in  a  vertical  direction  is  required;  and  second,  those  eases 
as  in  some  machine  tool  operations,  foundry  moulds,  punch 
presses,  and  assembly  work  where  in  addition  to  the  vertically 
downward  light  it  is  necessary  to  have  the  sides  of  the  work  ade- 
quately illuminated  by  means  of  side  components  of  the  light 
thrown  from  the  lamps  in  angular  directions,  a  feature  which  is 
dependent  on  the  size  of  the  room  and  somewhat  on  the  reflec- 
tion from  walls  with  the  over-head  system  of  lighting. 

It  is  important  in  each  of  these  cases  to  have  a  low  shadow 
effect.  In  that  class  where  the  surfaces  are  mostly  horizontal 
the  problems  are  usually  the  most  simple,  while  in  the  other  class 
where  the  sides  of  the  work  and  openings  must  be  cared  for, 
added  refinements  are  sometimes  necessary  to  produce  a 
satisfactory  result. 

Space  between  Floor  and  Ceiling. — Belting  and  other  obstacles 
may  exist  between  floor  and  ceiling  or  the  space  may  be  entirely 
free  from  obstruction.  Again,  there  may  be  much  dust  and  dirt 
in  the  air  as  in  the  foundry  or  blacksmith  shop,  and  here  special 
types  of  lamps  are  required  for  each  case.  The  open  spaces  sim- 
plify the  problems  and  make  possible  the  use  of  lamps  spaced 
comparatively  far  apart,  while  in  the  midst  of  belting  the  type  of 


102  FACTORY  LIGHTING 

lamp  and  the  spacing  must  be  such  as  to  reduce  the  shadows  other- 
wise cast  by  the  belts.  In  dusty  spaces,  a  penetrating  light 
must  be  employed  in  order  to  insure  adequate  illumination  on  the 
working  surfaces. 

Ceiling  Conditions. — The  installation  of  lamps  is  affected  by  the 
ceiling  construction  both  in  the  cost  of  wiring  and  in  the  reflection 
of  that  portion  of  the  light  which  may  reach  the  ceiling.  As 
shown  in  a  previous  chapter  the  ceilings  in  factory  buildings  may 
roughly  be  divided  into  those  of  wood,  concrete,  metal  and  the 
like,  a  distinction  being  made  between  plain  ceilings  and  those 
below  which  iron  work  projects  thus  dividing  the  ceilings  into 
sections  or  bays. 

Surroundings. — In  its  relation  to  the  net  illumination  on  the 
work,  the  color  and  condition  of  walls  and  the  work  has  a  consid- 
erable bearing.  With  dark  surroundings  a  larger  number  of 
lamps,  or  lamps  of  greater  candle-power  than  otherwise  are  neces- 
sary to  produce  satisfactory  results.  With  very  large  machines 
of  a  dark  nature,  the  effect  is  to  dampen  out  the  resulting  illumina- 
tion in  such  a  way  as  to  call  for  very  much  higher  intensities  than 
would  be  the  case  with  lighter  surfaces. 

68.  General  Requirements. — The  following  requirements  for 
factory  lighting  are  made  all  the  more  important  by  the  peculiar 
limitations  and  conditions  in  factory  buildings  and  in  factory 
work: 

(1)  Sufficient   illumination   should   usually   be   provided   for 
each  workman  irrespective  of  his  position  on  the  floor  space. 

(2)  The  lamps  should  be  installed  and  selected  so  as  to  avoid 
eye  strain  to  the  workmen. 

(3)  The  lamps  should  be  operated  from  circuits  which  will  in- 
sure reliable  illumination  facilities,  particularly  on  account  of  the 
demoralizing  effect  produced  by  intermittent  service  just  when 
the  light  is  most  needed. 

(4)  Adequate   illumination   should   be  provided    from   over- 
head lamps   in  such  measure  that  individual  carbon  filament 
lamps  close  to  the  work  may  be  unnecessary  except  in  special 
cases. 

(5)  The  type  and  size  of  lamp  should  be  adapted  to  the  particu- 
lar ceiling  height  and  class  of  work  in  question. 

(6)  In  addition  to  the  illumination  provided  by  over-head 
lamps,  individual  lamps  of  the  carbon  filament  type  should  be 
placed  close  to  the  work  if  they  are  absolutely  necessary,  and  in 


FACTORY  LIGHTING  103 

such  cases  the  lamp  should  be  provided  with  a  suitable  opaque 
reflector. 

These  requirements  may  now  be  met  by  means  of  the  new  types 
of  lamps,  one  type  of  which  can  usually  be  found  for  practically 
every  factory  location  and  adapted  to  general  physical  conditions 
typified  by  clearance  between  cranes  and  ceiling  and  other  similar 
items. 

69.  Method  of  Lighting  by  Over -head  Lamps. — The  mounting 
of  lamps  over-head  in  such  numbers  as  to  eliminate  the  need  for 
individual  lamps,  is  referred  to  as  the  over-head  method  of  light- 
ing. This  system  possesses  many  features  which  make  is  particu- 
larly well  adapted  to  factory  conditions,  and  by  the  proper  choice 
of  the  size  of  the  lamp  and  its  mounting,  results  can  be  secured 
which  will  conform  to  the  requirements  just  enumerated.  The 
many  advantages  of  this  over-head  method  when  compared  to 
the  use  of  individual  lamps  close  to  the  work,  commend  it  for 
general  adoption.  Its  superior  features  may  be  stated  as 
follows: 

The  over-head  lamps  may  be  made  to  furnish  adequate  ilumi- 
nation  in  a  general  manner  over  the  entire  working  surface,  thus 
permitting  work  to  be  done  at  every  portion  of  the  floor  space, 
rather  than  to  limit  the  work  to  certain  specific  points  under  in- 
dividual lamps. 

The  glare  of  the  lamp  if  too  close  to  the  work,  is  practically 
eliminated  by  mounting  the  lamps  well  above  the  heads  of  the 
workmen.  Further,  this  glare  from  lamps  close  to  the  work  is 
accentuated  by  the  fact  that  the  light  is  usually  on  a  small  por- 
tion of  the  work  only.  Comparative  darkness  in  the  neighboring 
space  about  this  bright  spot  makes  it  difficult  to  find  tools  and 
material,  and  in  addition  to  reducing  the  efficiency  of  the  work- 
man to  this  extent,  there  is  a  strain  on  the  eye  which  is  largely 
avoided  if  the  entire  working  surface  is  liberally  illuminated. 

The  maintenance  of  over-head  lamps  is  definite  and  clear  cut 
as  compared  to  the  individual  lamp  method,  and  may  be  con- 
ducted by  a  central  maintenance  division,  generally  with  better 
results  and  at  a  lower  cost  per  man,  taking  into  account  the 
improved  condition  of  the  lighting  from  over-head  lamps  in 
making  such  a  comparison.  The  appearance  of  the  factory 
where  all  drop  cords  are  removed  is  incidentally  greatly  improved, 
and  the  illumination  furnished  from  lamps  near  the  ceiling 
gives  to  the  entire  space  a  neat  and  pleasing  appearance,  in 


104  FACTORY  LIGHTING 

marked  contrast  to  locations  equipped  with  many  drop  cords 
each  of  which  is  covered  with  a  metal  shade. 

Finally,  tests  have  shown  that  the  eyes  are  in  a  better  condi- 
tion for  vision  with  a  given  illumination  intensity  when  general 
illumination  is  provided  by  over-head  lamps  than  when  indi- 
vidual lamps  are  placed  close  to  the  object,  with  the  surround- 
ings comparatively  dark. 

70.  The  Field  of  Various  Types  of  Lamps. — Very  low  ceilings 
require  small  lamps,  while  high  ceilings  require  correspondingly 
larger  lamps.     The  tungsten  lamp  is  a  good  example  of  the  me- 
dium-sized lamp  which  has  done  so  much  for  the  intermediate 
ceiling  heights.     The  mercury  vapor  lamp  in  like  manner  is  well 
adapted  to  moderate  ceiling  heights,  while  lamps  of  the  flaming 
carbon  arc  type  serve  in  those  locations  where  the  ceiling  height 
is  20  ft.  and  higher.     There  is  a  wrong  tendency  to  generalize 
conclusions  regarding  the  use  of  one  type  of  lamp  for  all  factory 
conditions,  whereas  too  much  emphasis  cannot  be  placed  on  the 
fact  that  each  type  of  lamp  has  in  a  general  way  a  field  of  its  own, 
and  the  best  results  are  secured  by  the  selection  of  the  proper 
type  of  lamp  for  a  given  location  without  prejudice. 

71.  Glass  and  Metal  Reflectors  Compared. — The  question  is 
sometimes  raised  as  to  the  use  of  glass  reflectors  in  connection 
with  tungsten  lamps  for  factory  lighting.     The  question  is  one 
largely  of  economy  and  maintenance,  and  in  the  prevention  of 
glare  from  tungsten  lamps  when  not  provided  with  some  shielding 
reflector.     The  answer  to  such  a  question  may  either  be  from  a 
theoretical  standpoint  or  as  the  result  of  practical  experience 
with  both  types. 

In  large  installations  of  tungsten  lamps  there  has  been  an 
effort  to  establish  the  merits  for  both  glass  and  metal  reflectors 
by  equipping  lamps  in  adjacent  bays  with  glass  reflectors  in  one 
case  and  metal  reflectors  in  the  other.  It  has  been  found  almost 
invariably  that  if  the  choice  is  left  to  the  workmen  and  super- 
intendents, glass  reflectors  will  be  given  preference  over  the 
metal  mainly  on  account  of  the  added  cheerfulness  they  produce. 
If,  therefore,  the  first  cost  and  maintenance  cost  of  the  glass 
reflectors  is  practically  the  same  as  with  the  metal,  then  glass 
should  be  employed.  Glass  reflectors  on  the  market  are  capable 
of  producing  an  amount  of  illumination  equal  and  even  greater 
in  some  cases  than  that  produced  by  the  best  metal  reflectors, 
and  even  if  the  first  cost  is  somewhat  higher,  the  added  advantage 


FACTORY  LIGHTING  105 

of  glass  as  opposed  to  metal  is  usually  sufficient  to  make  the  small 
difference  in  cost  a  negligible  item.  This  factor  is  all  the  more 
noticeable  when  one  considers  that  the  reflector  itself  is  a  small 
part  of  the  total  cost  connected  with  the  wiring,  the  lamp  and 
its  reflector. 

As  regards  maintenance  with  glass  reflectors  it  may  be  stated 
that  under  rough  factory  conditions,  glass  reflectors  are  to-day 
used  by  the  thousands  with  but  a  small  increase  in  maintenance 
due  to  breakage.  Thus,  out  of  the  total  maintenance  cost  in 
one  large  installation  it  has  been  found  that  the  charges  may  be 
proportioned  as  follows: 

Renewals,  cost  of  lamps 75  per  cent. 

Renewals,  broken  reflectors 3  per  cent. 

Labor,  making  renewals  and  changing  re- 
flectors for  washing 16  per  cent. ' 

Labor,  reflector  washing 2  per  cent. 

Additional  indirect  charges 4  per  cent. 


Total 100  per  cent. 

Reflectors  will  not  be  classified  from  the  commercial  stand- 
point, but  the  following  items  should  be  considered  in  the  selec- 
tion of  every  type  of  reflector  for  factory  use: 

(1)  Utilization  efficiency;  how  much  does  the  reflector  con- 
tribute to  the  effective  illumination  on  the  work? 

(2)  The  effect  in  reducing  glare. 

(3)  Natural   deterioration   with   age   through   accumulations 
of  dust  and  dirt. 

(4)  Ease  in  handling  and  uniformity  of  manufacture. 

(5)  Physical  strength  and  the  absence  of  projections  which 
may  increase  the  breakage. 

A  study  of  the  various  reflectors  on  the  market  with  the  aid 
of  the  foregoing  items,  will  determine  what  reflectors  are  best 
adapted  to  given  conditions.  Regarding  the  third  item  in  the 
foregoing  list,  it  may  be  stated  that  under  comparative  tests 
in  service  the  accumulations  of  dust  and  dirt  on  glass  reflectors 
does  not  seem  to  be  any  greater  than  the  coating  of  dirt  which 
accumulates  on  the  inside  of  a  metal  reflector  in  the  same  length 
of  time. 

72.  Side  Lighting. — It  has  been  customary  in  the  past  to  meas- 
ure effectiveness  of  illumination  in  terms  of  the  vertically  down- 
ward component  of  the  light.  This  method  has  ignored  the  value 


106  FACTORY  LIGHTING 

of  side  components  in  their  relation  to  vertical  surfaces  and  open- 
ings in  the  side  of  the  work.  It  is  sometimes  more  necessary  to 
light  the  side  of  a  machine  or  the  side  of  a  piece  of  work  than  the 
horizontal  surface.  If,  then,  when  designing  a  factory  lighting 
system,  the  prime  object  is  the  production  of  the  greatest  amount 
of  downward  illumination,  it  may  happen  that  the  side  compo- 
nent is  so  small  that  the  sides  of  machines  and  of  the  work  are 
inadequately  lighted. 

Experience  indicates  that  there  are  two  general  ways  in  which 
to  secure  adequate  side  lighting.  One  of  these  methods  is  to 
lower  the  lamps,  and  the  other  is  to  use  a  broader  distributing  re- 
flector than  is  called  for  by  the  rules  which  consider  uniformity 
of  the  downward  illumination  only.  Side  walls  or  other  reflecting 
surfaces  will  of  course  modify  the  results.  Thus,  after  the  de- 
termination of  a  certain  type  of  reflector  for  producing  uniform 
vertically  downward  illumination,  it  may  be  found  that  more 
side  light  is  necessary,  and  this  extra  side  component  may,  as 
stated,  usually  be  secured  by  selecting  a  somewhat  more  dis- 
tributing reflector.  Broader  reflectors  are  apt  to  result  in  less 
downward  illumination,  and  will  sometimes  call  for  larger  lamps 
than  found  necessary  by  preliminary  calculations. 

As  an  illustration,  in  a  certain  lighting  system  a  vertically 
downward  intensity  of  3  foot-candles  was  deemed  sufficient  for 
the  work  involved.  Measurements  and  observations  showed 
that  the  side  light  was  not  sufficient.  In  this  particular  installa- 
tion it  was  found  necessary  to  produce  a  vertically  downward  in- 
tensity of  5  foot-candles  on  the  average  in  order  to  secure  an 
intensity  of  2  foot-candles  on  the  sides  of  the  work,  and  also  to 
use  a  somewhat  broader  distributing  reflector  than  at  first  chosen. 
Two  foot-candles  on  the  sides  of  the  work  was  sufficient  in  this  case 
where  bench  work  and  work  in  the  vise  on  small  machine  parts 
was  conducted. 

It  is  recommended  that  the  lamps  be  mounted  near  the  ceiling 
in  all  reasonable  cases  where  side  light  is  necessary,  and  that  the 
side  light  be  increased,  not  by  lowering  the  lamps,  but  through 
the  medium  of  broader  distributing  reflectors  and  larger  lamps 
if  required.  This  stand  is  taken  on  account  of  the  glare  which 
results  when  the  lamps  are  mounted  too  close  to  the  work,  a  fea- 
ture most  noticeable  by  the  absence  of  a  reflector  or  where  glass 
reflectors  are  used. 

73.  The  Lighting  Circuits. — The  question  of  lighting  circuits 


FACTORY  LIGHTING  107 

• 

has  already  been  discussed  but  is  here  mentioned  with  particular 
reference  to  factory  conditions  where  motor  loads  are  apt  to  be 
large  in  comparison  to  the  energy  consumption  for  electric  lamps. 
In  some  cases  the  proportion  of  motor  load  to  lighting  load  is  in 
the  ratio  of  10  to  1,  in  others  7  to  1,  and  so  on,  and  the  varying 
demands  on  the  circuits  by  motors  may  greatly  affect  the  lamps. 
Hence  it  is  important  to  maintain  strictly  separate  supply  circuits 
for  the  lamps  in  order  to  avoid  the  varying  voltage  apt  to  result 
if  the  motors  are  connected  to  the  same  circuits. 

In  addition  to  the  superior  illumination  resulting  from  lamps 
supplied  from  constant  voltage  mains,  some  types  operate  with 
longer  life  or  very  much  better  mechanically  when  supplied  with 
constant  voltage  than  otherwise.  These  features  will  therefore 
generally  more  than  offset  the  somewhat  greater  cost  of  maintain- 
ing separate  circuits  for  each  class  of  service. 

74.  A  Practical  Case  in  a  Location  with  Moderate  Ceiling 
Height. — As  a  typical  example  of  factory  lighting,  a  moderate 
ceiling  height  of  13  ft.  6  in.  is  considered.  The  building  is  divided 
into  bays  16  by  23  ft.  and  one  of  these  typical  bays  is  shown  in 
Fig.  65.  The  walls  and  ceilings  are  light  in  color,  thus  aiding  the 
net  illumination.  The  work  may  be  classed  as  bench  work 
where  adequate  side  light  is  required;  also  machine  work,  where 
some  line  shafting  and  belting  form  an  obstruction  to  the  illumina- 
tion; and  some  assembly  work  where  side  light  is  required. 

The  ceilings  are  of  wood,  and  hence  wood  moulding  may  be 
used,  while  the  switches  may  be  located  on  central  columns  in 
easy  reach  of  the  workman  from  the  floor.  The  various  switches 
are  wired  through  the  medium  of  conduit  running  down  the  con- 
crete columns,  and  iron  outlet  boxes  serve  the  double  purpose  of 
supporting  the  snap  switch,  and  supplying  a  wall  receptacle  at 
each  column  as  an  outlet  for  extension  lines  when  necessary. 
After  numerous  experiments,  an  arrangement  of  tungsten  lamps 
as  shown  in  Fig.  65  was  found  to  supply  the  required  vertically 
downward  intensity  of  illumination.  The  relation  of  the  spac- 
ing distance  to  the  mounting  height  called  for  a  concentrating 
reflector  in  order  to  produce  uniform  downward  illumination  as 
previously  explained,  but  the  requirements  of  side  light  for  many 
of  the  kinds  of  work  made  it  necessary  to  use  a  somewhat  more 
distributing  reflector  than  called  for  by  rules  of  the  reflector  com- 
panies, that  is,  an  intensive  type  instead  of  a  focusing  type  in  this 
case.  Glass  reflectors  are  also  used  to  give  a  cheerful  appearance 


108 


FACTORY  LIGHTING 


to  the  factory  spaces  as  an  incidental  advantage,  and  where  the 
ceiling  is  light  in  color  that  portion  of  the  light  which  is  transmitted 
through  the  glass  to  the  ceiling  is  in  turn  reflected  to  the  work 
thus  adding  to  the  resulting  illumination. 

On  account  of  the  various  requirements  throughout  this  factory 
higher  intensities  of  illumination  are  required  in  some  parts  than 


II. 


FIG.  65. — Plan  and  elevation  of  bay  in  a  typical  factory  location  showing 
arrangement  of  the  100- watt  tungsten  lamps  over-head. 

in  others,  and  the  arrangement  of  lamps  is  well  adapted  to  this 
end,  for  by  using  smaller  lamps  in  the  outlets  the  intensity  is  re- 
duced without  in  any  way  affecting  the  uniformity  provided  the 
size  of  the  reflector  always  corresponds  to  the  size  of  the  lamp. 

The  lamps  are  mounted  at  the  ceiling  to  avoid  glare  and  the 
appearance  in  this  particular  location  is  thus  greatly  benefited. 
Fig.  65  shows  that  the  lamps  are  distributed  in  a  symmetrical 
manner  with  respect  to  the  bays,  and  the  wiring  was  thus  sim- 


FACTORY  LIGHTING 


109 


plified  because  the  circuits  could  be  confined  to  the  separate  bays, 
that  is,  one  circuit  per  bay.  This  makes  it  unnecessary  to 
extend  the  wires  under  girders  in  order  to  feed  the  lamps  in 
adjacent  bays. 

The  size  of  the  bays  seemed  to  favor  the  control  of  six  lamps 
per  switch,  but  the  requirements  of  the  workmen  near  the  center 
of  the  building  made  artificial  lighting  necessary  so  often  when 
the  men  near  the  windows  were  still  supplied  with  sufficient 
light,  that  the  two  lamps  in  each  bay  nearest  the  window  were 


FIG.  66. — Reproduced  from  a  photograph  taken  at  night  under  the  arti- 
ficial light  from  100-watt  tungsten  in  a  typical  factory  location. 

controlled  from  one  switch,  while  the  four  remaining  lamps 
in  the  outside  bays  were  controlled  from  a  second  switch  and  the 
six  lamps  in  the  central  bay  were  each  controlled  from  a  third 
switch,  and  so  on. 

The  intensity  of  both  vertically  downward  and  side  compo- 
nents of  the  illumination  is  such  that  practically  no  individual 
lamps  are  necessary  even  for  the  machine  work,  thus  removing 
the  necessity  for  the  maintenance  of  drop  cords  and  sockets 
near  the  machinery.  Fig.  66  shows  a  view  of  a  factory  location 
where  the  lighting  has  been  installed  according  to  the  foregoing 


110  FACTORY  LIGHTING 

description,  and  some  idea  of  the  uniformity  of  the  illumination 
is  given  by  the  illustration,  also  the  neat  appearance  of  the  over- 
head system  and  the  added  cheerfulness  produced  by  the  reflec- 
tion from  walls,  columns  and  ceilings.  Figs.  67  and  68  show 
other  typical  factory  lighting  systems  where  modern  illumina- 
tion design  has  been  applied. 

75.  A  Practical  Case  in  a  Location  Where  the  Lamps  Must 
be  Mounted  Very  High. — As  an  illustration  of  a  case  where  the 
mounting  height  of  the  lamps  is  determined  by  the  crane  near 


FIG.  67. — Reproduced  from  a  photograph  taken  at  night  under  the  arti- 
ficial from  300  candle-power  mercury  vapor  lamps  in  a  typical  factory 
location. 

the  over-head  iron  work  of  the  building,  a  factory  space  is  taken 
where  the  distance  from  floor  to  girder  line  is  50  ft.  The  loca- 
tion is  divided  into  bays  16  by  70  ft.,  several  of  these  bays  being 
shown  in  Fig.  69.  There  is  no  regular  ceiling  because  of  the  open 
girder  construction,  and  the  walls  and  surroundings  are  dark. 

The  work  consists  of  large  machine  tool  operations  and  heavy 
assembly,  and  here  the  vertically  downward  as  well  as  the  side 
light  must  be  adequate.  The  absence  of  a  ceiling  from  which 
to  support  the  lamps  and  the  small  clearance  between  the  crane 


FACTORY  LIGHTING 


111 


and  the  iron  work  makes  it  necessary  to  mount  the  lamps 
on  specially  constructed  wire  supports.  The  latter  scheme  was 
used  on  account  of  the  advantage  to  be  derived  in  pulling  the 
lamps  into  a  central  point  for  trimming.  The  control  circuits 
are  run  down  the  structural  columns  to  a  point  accessible  from 
the  floor,  the  switch  loops  being  run  in  iron  conduit  which  is 
attached  to  the  columns. 

On  account  of  the  mounting  height,  a  large  lamp  is  necessary 
because  of  the  volume  of  light  needed  to  produce  the  required 


FIG.  68. — Reproduced  from  a  photograph  taken  at  night  under  the  artificial 
light  from   100  watt  tungsten  lamps  in  a  typical  factory  location. 

effect  on  the  work,  and  also  to  reduce  the  maintenance  which 
may  be  somewhat  high  if  a  large  number  of  small,  lamps  are 
distributed  at  such  heights.  Two  rows  of  arc  lamps  of  the  flame 
carbon  type  are  arranged  in  alternate  bays  so  as  to  be  staggered, 
and  the  control  circuits  include  the  lamps  on  one  side  only  in 
each  case,  so  that  the  operation  of  the  lamps  in  either  row  is 
independent  of  the  other.  This  scheme  has  the  advantage  of 
steadying  the  illumination,  when  a  momentary  failure  of  the  lamps 
on  one  circuit  might  otherwise  greatly  reduce  the  net  lighting 
effect.  Fig.  69  shows  the  arrangement  in  several  bays,  and  also 


112 


FACTORY  LIGHTING 


the  mounting  by  means  of  the  wire  supports,  which  extend  from 
the  center  of  aisle  to  the  walls  on  either  side. 

This  arrangement  and  the  size  of  lamps  produce  a  good  illumi- 
nation on  the  work  nearly  50  ft.  below  the  lamps,  and  the  qual- 
ity of  the  light  is  such  as  to  penetrate  the  large  distance  in  an 
exceptional  manner.  The  low  maintenance  of  the  long  burning 


Elevation 


Girder  Line  ' 


Plan 

FIG.  69. — Plan  and  elevation  of  several  bays  in  a  typical  factory  where 
high  mounting  of  lamps  is  necessary.     Flame  carbon  arc  lamps  used. 

flame  carbon  arc  lamp  makes  it  an  economical  unit  and  its  use 
in  cases  of  this  kind  is  apt  to  be  quite  satisfactory. 

76.  Other  Items. — The  items  connected  with  the  selection  of 
the  type  of  lamp,  the  mounting  height  and  the  spacing  distance 
have  been  described  in  a  previous  chapter,  and  a  reference  to 


FACTORY  LIGHTING  113 

that  treatment  should  be  made  in  the  design  of  factory  lighting 
systems.  All  the  points  brought  out  in  that  chapter  are  appli- 
cable to  factory  lighting,  and  possibly  greater  emphasis  should 
be  placed  on  the  following  of  the  principles  of  illumination  design 
for  factory  lighting  than  for  other  classes  of  lighting. 

The  maintenance  items  discussed  in  a  previous  chapter  apply 
also  in  an  exceptional  manner  to  the  conditions  in  factory  build- 
ings, and  so  great  is  the  importance  of  these  problems  in  connec- 
tion with  lighting  systems  in  the  factory  that  they  may  be  said 
to  form  one  of  the  major  items  in  the  furnishing  of  adequate  light. 
The  installation  of  the  system  according  to  a  scientific  design 
is  naturally  most  important,  but  the  maintenance  of  the  lamps 
so  as  to  keep  the  system  up  to  the  same  excellence  from  month 
to  month  is  equally  important. 

77.  Cost  Factors. — The  shop  manager  is  concerned  with  the 
value  of  the  artificial  light  in  relation  .to  the  factory  output, 
and  hence  looks  for  a  return  both  in  quantity  and  quality  of 
work  as  a  direct  result  from  the  expense  of  a  modern  system  of 
illumination. 

The  value  of  adequate  light  can  easily  be  reduced  to  the  time 
saved  by  employees  in  the  performance  of  given  work,  in  im- 
proved accuracy  of  workmanship,  in  the  protection  afforded 
the  eyes  of  the  workmen,  and  in  the  beneficial  effect  on  tempera- 
ment produced  by  brighter  and  more  cheerful  surroundings 
as  well  as  in  the  decrease  in  accidents  and  greater  safety.  If, 
therefore,  improved  light  is  interpreted  into  the  equivalent  time 
saved  by  employees  in  the  various  shop  operations  due  to 
all  these  elements,  the  equivalent  wages  or  the  larger  and 
better  output  as  the  case  may  be,  can  then  be  classed  as  a 
distinct  asset  to  the  plant  through  the  medium  of  improved 
illumination.  Fig.  64  shows  graphically  these  relations  between 
wages  and  lighting  costs. 

As  a  starting  point,  therefore,  in  the  economy  of  factory  light- 
ing, a  proper  attitude  should  be  taken  to  the  accompanying 
improvement  in  quality  and  quantity  of  workmanship  through 
the  usefulness  of  the  light,  to  the  exclusion  in  a  degree  of  emphasis 
on  the  relative  cost  values  of  the  light  itself.  If  the  entire  light- 
ing question  can  be  viewed  rather  as  an  asset  to  the  output  of 
the  plant  in  the  study  of  the  merits  of  various  types  of  illumina- 
tion, than  in  the  directing  of  all  attention  to  minor  differences  in 
first  cost  and  operation  expense,  the  needs  for  legislative  insistence 


114  FACTORY  LIGHTING 

on  improvements  of  lighting  conditions  will  become  a  secondary 
influence. 

As  a  matter  of  fact,  many  of  the  present  conditions  are  so 
changed  over  former  factory  surroundings  that  the  idea  of  light- 
ing as  an  asset  to  production  has  begun  to  be  taken  as  a  definite 
working  basis.  The  factory  manager,  whose  buildings  are 
equipped  with  modern  lighting,  prides  himself  on  the  improved 
appearance,  while  he  gains  in  the  improved  workmanship  and 
the  greater  contentment  among  employes,  all  directly  resulting 
from  a  higher  standard  of  environment. 


CHAPTER  VIII 
POWER-HOUSE  LIGHTING 

78.  Relations  of  Lighting  to  Operation. — Reliable  operation 
in  power  plants  demands  the  use  of  every  available  resource  to 
that  end.     Investments  in  switchboard  appliances  for  the  control 
of  circuits  are  considered  an  asset  to  the  station  equipment, 
and  so  great  is  the  importance  of  continuity  of  service  that  central 
stations  spare  no  reasonable  expense  for  maintaining  continuous 
operation. 

Throughout  the  day  and  night  there  are  many  intervals 
during  which  artificial  light  is  required.  Repairs  to  broken 
down  machines  must  usually  be  made  with  the  utmost  dispatch 
and  every  facility  should  be  provided  to  aid  the  rapidity  with 
which  such  work  is  accomplished.  This  feature  is  emphasized 
by  the  tendency  to  broaden  the  responsibility  of  each  employe 
to  include  a  large  amount  of  expensive  apparatus  in  the  station 
service.  To  permit  each  man  to  fulfil  his  duties  makes  it  there- 
fore all  the  more  necessary  that  the  best  artificial  light  available 
be  provided. 

79.  General   Requirements. — In  the   lighting  of  the  power 
house  several  requirements  should  be  made  the  object  of  study: 

(1)  Sufficient  illumination  at  all  points  of  the  floor  space  for 
general  operation,  inspection  and  repairs  to  machines. 

(2)  An  arrangement  of  lamps  which  will  distribute  the  light 
to  the  various  parts  of  the  machines  making  them  readily  visible 
at  all  times. 

(3)  The  elimination  of  dense  shadows  by  a  sufficient  number 
of  lamps  properly  mounted. 

(4)  Absolute  reliability  even  when  the  station  is  temporarily 
disabled. 

(5)  An  arrangement  of  individual  lamps  which  will  furnish 
suitable  light  to  valves,  gauges,  and  switchboard  instruments. 

In  overhauling  steam  and  electrical  equipment  it  is  desirable 
that  the  various  openings  in  and  about  the  machinery  be  suitably 
lighted,  and  the  sides  of  apparatus  must  be  given  due  weight  in 

115 


116  FACTORY  LIGHTING 

properly  directing  the  light,  because  these  parts,  with  ordinary 
methods  of  lighting,  are  often  in  comparative  darkness,  either  on 
account  of  a  lack  of  side  light,  or  due  to  excessive  shadows, 
which  amounts  to  the  same  result. 

80.  Economy   Afforded    by    Good   Lighting. — As    previously 
implied,  the  successful  operation  of  central  stations  and  other 
power  houses  is  promoted  by  adequate  and  reliable  types  of 
steam  and  electrical  equipment,  by  a  suitable  arrangement  of 
machinery,  the  coal  and  water  facilities,  ventilation,  and  artificial 
light  of  an  intensity,  quality,  and  distribution  to  serve  as  an  aid 
in  the  operation  of  the  plant  during  dark  days  and  at  night  and 
thus  facilitate  repairs  and  emergency  work  in  the  continuous 
operation  of  the  plant. 

The  central  station  is  looked  upon  as  the  source  from  which 
energy  for  light  and  power  is  to  be  derived  for  the  public,  and 
a  fact  which  has  to  some  extent  been  overlooked  in  the  past  is 
that  the  station  itself  requires  light  of  suitable  quality  and  relia- 
bility in  the  economy  of  its  own  operation.  A  shut  down  in  the 
power  station  connected  with  a  factory,  due  to  an  accident  or  to 
other  causes,  involves  considerably  more  inconvenience  and 
greater  losses  of  time  and  money  than  perhaps  any  other  similar 
auxiliary  to  the  factory  operation.  No  element  of  the  equip- 
ment, therefore,  should  be  overlooked  in  the  attempt  to  secure 
that  continuity  of  service  which  aids  reliability  of  operation. 

Again,  the  power  plants  connected  with  the  factory  -provide 
not  only  the  artificial  light  but  usually  all  the  motive  power 
for  machine  tools  and  other  purposes,  and  a  shut  down  of  several 
minutes  often  involves  losses  of  hundreds  of  dollars  in  output 
which  must  obviously  be  charged  to  the  power  house.  The 
avoidance  of  such  difficulties  is  a  problem  met  by  every  station 
superintendent  connected  with  industrial  plants. 

81.  The  Modern  Viewpoint. — In  the  past  power-house  lighting 
has  been  neglected  to  some  extent  due  to  a  lack  of  appreciation 
of  the  effect  of  sufficient  artificial  light  on  the  operation,  but 
due  also  in  large  measure  to  the  absence  of  suitable  lamps  for 
the  conditions  in  such  buildings.     As  already  stated,  both  of 
these  causes  are  now  giving  way  to   conditions  which  are  pro- 
ducing many  improvements  in  the  station  lighting  equipment. 
There  t  is^  certainly  a  deeper  appreciation  of  the  necessity  for 
adequate  light,  and  types  of  lamps  are  now  available  for  practi- 
cally every  condition  to  be  solved. 


POWER-HOUSE  LIGHTING  117 

A  recent  editorial  in  one  of  the  technical  journals  referred  to 
the  question  of  power  house  lighting  as  an  old  and  threadbare 
topic.  Neither  of  these  words  is  quite  in  place  because  while  the 
problems  in  one  sense  may  be  looked  upon  as  old  and  threadbare, 
they  deal  directly  with  economy  and  reliability  of  operation  and 
they  can  be  solved  in  new  ways  by  new  lamps.  A  commendable 
feature  in  the  editorial  is  the  emphasis  placed  on  the  neglect  of 
many  lighting  companies  to  look  to  their  own  lighting  while 
being  most  progressive  in  other  lines  of  their  equipment  as  well  as 
in  the  scientific  installation  of  lamps  in  establishments  of  their 
customers. 

It  is  believed  that  with  the  many  improvements  in  modern 
lighting  apparatus,  power  station  men  are  now  coming  to  a  posses- 
sion of  distinctly  new  ideas  regarding  efficiency  of  operation,  and 
that  these  ideas  are  beginning  to  include  not  only  the  generating 
apparatus  itself,  but  all  of  those  features  which  contribute  to  its 
maintenance  and  operation  in  the  best  possible  manner. 

82.  Various  Locations  Involved.  The  Engine  Room— A  typ- 
ical engine  room  consists  of  a  rather  long  and  relatively  narrow 
building  with  high  roof  trusses,  and  as  a  consequence  these 
buildings  lend  themselves  to  the  over-head  method  of  lighting. 
Difficulties  in  the  past  have  usually  been  an  insufficiency  of  light 
and  poor  distribution.  Fig.  70  indicates  an  efficient  method  of 
distributing  the  lamps  for  securing  sufficient  general  light  for 
attendance  and  repairs.  The  switch  control  used  in  this  in- 
stallation makes  possible  the  control  of  lamps  in  alternate  groups 
so  that  for  ordinary  purposes  a  moderate  intensity  is  available 
with  half  of  the  lamps,  and  a  higher  intensity  with  all  the  lamps 
turned  on  at  times  of  emergency  and  repairs.  This  arrangement 
of  lamps  insures  adequate  side  light  by  the  use  of  a  relatively 
large  number  of  medium-sized  units,  and  also  that  the  light  at  any 
one  point  on  the  floor  space  is  derived  from  numerous  sources, 
coming  in  many  directions  and  thus  reducing  marked  shadows. 
By  mounting  the  lamps  at  the  girder  line  glare  is  avoided. 

Probably,  the  most  important  item  is  absolute  reliability  of  the 
illumination  at  all  times.  To  secure  this  end,  the  lighting  circuit 
is  fed  from  a  source  entirely  separate  from  the  outgoing  feeders. 
In  some  cases  storage  batteries  are  installed  with  a  switch  in  the 
lighting  circuit  so  that  the  lamps  may  be  connected  to  this  emer- 
gency supply  when  required.  In  other  cases  a  small  number 
of  auxiliary  lamps  are  connected  to  the  exciter  circuit  as  a  further 


118  FACTORY  LIGHTING 

safeguard,  although  the  use  of  the  exciter  circuit  is  not  generally 
recommended. 

The  Boiler  Room. — Boiler  rooms  usually  consist  of  a  narrow 
passage  way  faced  either  on  one  or  both  sides  by  the  boilers,  on 
which  are  located  the  gauges.  The  piping,  stoking  apparatus  and 
valves  require  moderate  light,  and  the  lamps  used  for  this  pur- 
pose are  often  controlled  by  conveniently  located  switches  so 
that  they  may  be  turned  on  when  necessary.  Sufficient  light  is 
required  over  the  main  passage,  but  the  requirements  of  the  boiler 
room  are  sometimes  offset  by  the  firing  and  general  care  of  fur- 
naces, which  are  usually  in  themselves  sufficiently  lighted  by 
the  fires.  Some  side  light  on  the  front  of  boilers  and  furnaces  is 
necessary,  however,  and  it  is  desirable  to  eliminate  the  glare 
which  is  particularly  objectionable  with  the  dark  surroundings 
if  the  lamps  are  mounted  too  low. 

Coal  Bins  and  Conveyors. — In  those  boiler  rooms  equipped 
with  stoking  apparatus,  the  coal  bins  are  ordinarily  above  the 
boiler  room  and  must  be  accessible  for  some  attendance  and  in- 
spection. Here  an  adequate  number  of  lamps  should  be  provided, 
but  by  controlling  them  from  convenient  switches  they  need  be 
turned  on  only  during  the  times  of  actual  attendance  and  in- 
spection. Passages  through  which  the  coal  conveyors  run  must 
be  judiciously  lighted  for  preventing  accidents,  and  to  facilitate 
access  to  the  various  parts  of  the  equipment.  The  lamps  should 
be  so  located  as  to  be  safe  from  accidental  breakage. 

Basement. — The  basement  usually  has  a  fairly  low  ceiling  and 
is  apt  to  be  crowded  with  pumps  and  condensers.  This  apparatus 
sometimes  extends  from  the  floor  to  the  ceiling,  making  the 
lighting  difficult.  In  fact,  general  lighting  is  in  many  cases  out 
of  the  question,  and  individual  lamps  must  then  be  located  at 
those  points  where  they  will  be  the  most  useful. 

The  installation  of  wiring  and  lamps  must  be  made  to  with- 
stand the  dampness  and  conduit  work  is  possibly  the  best  means 
for  running  the  wires.  On  account  of  the  low  head  room  and 
the  usual  crowded  conditions,  small  lamps  in  large  numbers  are 
preferable. 

Transformer,  Oil  Switch  and  Bus-bar  Compartments. — The  loca- 
tion of  this  apparatus  is  often  in  compartments  separated  from 
the  main  engine  room  by  concrete  or  brick  walls,  and  only  a 
meager  quantity  of  artificial  light  is  required  for  the  ordinary 
purposes.  However,  a  sufficient  number  of  lamps  should  be  in- 


POWER-HOUSE  LIGHTING 


119 


stalled  to  permit  of  fairly  high  illumination  at  those  times  when 
the  compartments  are  inspected  or  when  repairs  are  necessary. 
Carbon  filament  lamps  may  be  used,  although  tungsten  lamps 
may  also  be  employed  to  advantage. 

83.  A  Practical  Case  where  Medium-sized  Lamps  are  Used. — 
To  illustrate  the  items  involved,  a  typical  power  house  as  shown  in 
Fig.  70  is  selected.  The  floor  dimensions  are  75  by  128  ft.  and 


Elevation 

128- 


— 16---H 


& 


Switch 
board./ 


Plan 

FIG.  70. — Plan  and  elevation  of  typical  power  house  showing  arrangement 
of  250-watt  (200  candle-power)  tungsten  lamps  equipped  with  Holophane 
" Focusing"  type  glass  reflectors. 

the  ceiling  height  is  21  ft.  This  ceiling  height  may  be  classed  as 
moderate  and  medium-sized  lamps  are,  for  this  reason,  the  best. 

This  station  was  poorly  lighted  formerly  by  six  rather  large 
lamps  spaced  about  32  ft.  apart  and  mounted  at  the  ceiling. 
This  original  arrangement  is  shown  in  Fig.  71,  and  the  complaints 
from  the  lighting  were  somewhat  as  follows: 

(1)  The  illumination  was  so  inadequate  as  to  cause  much 
difficulty  in  the  routine  work  of  attendance  and  in  emergency 
work  on  dark  days  and  at  night. 


120 


FACTORY  LIGHTING 


(2)  As  usual  in  such  cases,  the  very  small  number  of  large 
lamps    with    the    large    spacing    distances    produced    excessive 
shadows.     Extension     lines     were     required,    therefore,    when 
making  repairs  on  the  apparatus,  involving  losses  of  time  through 
the  handling  of  individual  lamps. 

(3)  The  service  was  unreliable  and  somewhat  intermittent 
due  to  voltage  conditions  because  the  lamps  were  fed  from  the 
regular  service  mains. 


j      "5   x      r¥1      rW 

L. 

Elevation 

12S                                                                             >] 

||  j 

H 

H 

H 

3 
•5 

• 

• 

ft 

tt 

H 

Plan 

FIG.  71. — Plan  and  elevation  of  the  typical  power  house  shown  in  Fig. 
70  indicating  here  the  old  arrangement  of  lamps.  Compare  with  Fig.  70. 
In  the  installation  shown  above  enclosed  carbon  arc  lamps  were  used. 

The  Improved  Arrangement. — In  Fig.  70  is  shown  the  improved 
arrangement  where  250-watt  tungsten  lamps  are  used.  A  com- 
parison with  Fig.  71  shows  that  the  spacing  of  the  lamps  is  greatly 
reduced,  thus  improving  the  directional  features  of  the  light. 
The  service  from  this  new  scheme  resulted  in  the  following 
advantages : 

(1)  Uniform  illumination  over  the  entire  station  with  adequate 
side  light  on  vertical  surfaces  of  the  machines. 


POWER-HOUSE  LIGHTING  121 

(2)  The  large  number  of  lamps  eliminates  marked  shadows 
and  facilitates  the  work  in  and  about  tall  machines. 

(3)  The  control  arrangement  is  flexible,  and  alternate  rows  of 
lamps  may  be  turned  on  for  general  purposes,  while  for  emergency 
all  of  the  lamps  may  be  used.     It  will  be  noted  that  even  with 
half  of  the  lamps  turned  on  in  alternate  rows,  the  intensity  of 
the  illumination  is  fairly  uniform. 


FIG.  72. — Reproduced  from  a  photograph  taken  at  night  under  the  arti- 
ficial light  from  250-watt  (200  candle-power)  tungsten  lamps  and  Holo- 
phane  "Focusing"  type  glass  reflectors  as  shown  in  Fig.  70. 

(4)  By  mounting  the  lamps  near  the  ceiling,  glare  is  avoided 
because  the  lamps  are  well  above  the  line  of  vision. 

All  wiring  is  placed  in  conduit  and  by  the  use  of  waterproof 
sockets  the  wires  are  protected  from  bad  effects  due  to  dampness. 
In  this  case  the  supply  circuit  for  the  station  lamps  is  fed  from  a 
separate  lighting  transformer,  and  a  special  switch  is  provided  for 
throwing  the  lamps  to  a  steam-driven  exciter.  For  reasons 
already  stated,  the  rule  has  been  followed  of  keeping  the  lighting 
circuits  entirely  separate  from  the  station  switchboard. 

A  remarkable  difference  was  noted  in  this  particular  case 
between  the  appearance  of  the  old  and  the  new  lighting  schemes. 


122 


FACTORY  LIGHTING 


Elevation 


A  view  of  the  station  at  night  taken  under  the  artificial  light 
is  shown  in  Fig.  72,  which  shows  to  some  extent  the  absence  of 

marked  shadows  and  the  uniformly  distributed 

lighting  effect. 

84.  Arc  Lamps  and  Mercury  Vapor  Lamps. 
— A  power  house  with  a  ceiling  height  of  40 

^  ft.  and  floor  area  of  63  by  168  ft.  is  shown  in 

Fig.  73.  As  previously  explained,  the  need 
for  a  large  number  of  lamps  decreases  some- 
what as  the  ceiling  height  increases,  and  hence 
for  a  mounting  height  of  40  ft.,  lamps  of  large 
size  are  permissable  and  may  be  arranged  to 
produce  results  comparable  with  those  pro- 
duced by  smaller  lamps  when  mounted  lower. 

Here  it  is  planned  to  use  lamps  of  the 
long-burning  flame  carbon  arc  type  as  shown 
in  the  illustration.  These  lamps  are  to  be 
supplied  from  a  separate  lighting  circuit  and 
the  control  by  the  alternate  scheme  permits 
the  use  of  a  portion  of  the  lamps  only,  or  all 
as  the  needs  require. 

Mercury  vapor  lamps  are  also  particularly 
well  adapted  to  many  cases  of  power-house 
lighting,  and  numerous  instances  are  to  be 
found  where  this  type  of  lamp  is  in  service  for 
power-house  lighting  purposes. 

85.  Simple    Principles    Important. — From 
the  foregoing  illustrations  the  station  superin- 
tendent will  realize  that  the  expense  for  suffi- 
cient artificial  light  is  a  small  item  when  com- 
pared with  the  saving  in  labor  and  the  avoid- 
ance of  losses  in  time  in  the  general  operation 
and  upkeep  of  the  station.     It  is  also  apparent 
that  the  choice  of  lamp  is  largely  dependent 
on  the  surroundings  and  on  the  ceiling  height. 
Where  incandescent  lamps  are  mounted  low 
they  should  always  be  provided  with  suitable 
shielding  reflectors  so  as  to  reduce  glare,  but 
the  most  advantageous  way  to  overcome  glare 

is  to  mount  the  lamps  sufficiently  near  the  ceiling  to  place  them 
above  the  line  of  vision. 


n 


H 


H 


B 


n 


B 


lis 

*v 


Plan 

FIG.  73.— Plan 
and  arrangement  of 
a  typical  power 
house  showing  ar- 
rangement for  the 
use  of  flame  car- 
bon arc  lamps  (long 
burning) .  This 

represents  the  use 
which  may  be 
made  advantage- 
ously of  large  lamps 
for  high  ceilings. 


POWER-HOUSE  LIGHTING  123 

Flexibility  of  control  is  an  item  to  incorporate  in  the  original 
plans,  but  if  the  lamps  are  to  be  installed  without  set  plans,  care 
must  be  taken  to  arrange  the  circuits  so  that  the  lamps  may 
be  controlled  in  a  flexible  manner,  and  that  for  low  intensities, 
that  is,  where  a  portion  only  of  the  lamps  is  used,  the  light  may 
be  uniformly  distributed.  It  is  specially  important  to  control 
a  few  lamps  from  a  single  switch  so  that  lamps  not  required  may 
be  turned  out  without  affecting  too  large  a  portion  of  the  floor 
space. 

86.  Definite  Rules  are  Apt  to  Mislead. — The  practical  operator 
naturally  looks  for  definite  rules  on  which  to  base  the  plans 
for  new  lighting.  This  is  not  only  difficult  in  lighting  work  on 
account  of  the  many  factors  involved,  but  may  even  be  objection- 
able on  account  of  the  tendency  to  use  such  rules  without  due 
regard  to  the  obtaining  of  the  best  results.  If  the  ceilings  and 
walls  are  dark,  either  more  or  larger  lamps  are  required  than  if 
these  parts  of  the  building  are  painted  white. 

The  foregoing  general  items  are  intended  to  give  an  idea  of 
the  requirements  and  should  enable  the  station  superintendent  to 
plan  for  the  new  lighting  system  or  will  show  the  importance  of 
obtaining  expert  advice  for  securing  desired  results. 

Intensity  Required. — The  simplest  test  of  any  lighting  instal- 
lation is  the  answer  to  the  question  "how  well  can  the  objects  be 
seen?"  but  a  safe  conclusion  can  be  reached  only  after  the  illum- 
ination has  been  worked  under  for  a  considerable  time.  Con- 
clusions reached  after  a  casual  glance  should  never  be  depended 
upon.  Another  objection  to  using  this  common  sense  test  is 
that  practically  every  individual  has  his  own  idea  of  the  amount 
of  light  required  for  given  purposes,  and  what  may  be  adequate 
in  the  estimation  of  one  person  may  seem  inadequate  to  another. 
The  solution  of  the  problem  must  then  be  in  obtaining  an  average 
which  is  satisfactory  to  the  normal  eye. 

Based  on  tests  conducted  in  various  power  houses,  it  may  be 
stated  that  for  average  conditions  from  2  to  3  foot-candles  are 
adequate.  In  some  cases,  however,  power  houses  are  operated 
with  an  intensity  but  slightly  over  1  foot-candle.  This  latter 
value  under  average  conditions  is  somewhat  low,  particularly 
when  the  artificial  light  must  be  used  at  various  times  on  dark 
days  as  well  as  at  night.  The  point  cannot  be  too  strongly  empha- 
sized that  the  walls  and  ceilings  should  be  a  light  color  so  as  to 
augment  the  artificial  light  by  their  reflecting  surfaces. 


124  FACTORY  LIGHTING 

87.  Maintenance. — As  explained  in  a  previous  chapter  the 
maintenance  work  is  as  important  in  the  lighting  equipment  of 
the  power  house  as  elsewhere.     Reflectors  used  with  tungsten 
lamps  should  be  cleaned  at  fairly  frequent  intervals,  and  burned 
out  or  otherwise  defective  lamps  renewed  or  repaired  systematic- 
ally.    The  various  details  of  this  work  have,   however,  been 
explained  at  length  in  the  chapter  under  that  subject. 

88.  General  Hints. — In   order  to   aid  the  practical   station 
man  it  may  be  stated  that  the  size  of  lamps  should  always  be 
adapted  to  the  ceiling  or  mounting  height.     It  is  best  to  space 
the  lamps  symmetrically,  that  is,  in  squares  or  in  rectangles, 
depending  on  the  length  and  width  of  each  bay.     As  before  in- 
dicated, mount  the  lamps  sufficiently  high  to  avoid  glare,  and  if 
tungsten  lamps  are  employed  always  use  a  reflector  and  compen- 
sate for  the  increased  height  with  high  ceilings  by  the  use  of  a 
concentrating  reflector. 

Water  gauges  have  been  the  subject  of  some  attention  in  con- 
nection with  their  proper  lighting,  and  several  devices  have  been 
suggested  for  taking  care  of  this  unique  case.  Dirt  accumulations 
on  the  glass  often  make  the  water  level  difficult  to  see,  and  for  this 
reason  the  lighting  may  be  intensified  to  some  extent  by  suspend- 
ing a  piece  of  white  cardboard  or  a  white-painted  metal  shield 
behind  the  glass  so  that  the  water  level  may  be  read  by  the  con- 
trast thus  afforded. 

89.  Summary. — The  foregoing  instances  are  given  as  examples. 
Before  attempting  to  utilize  the  results  as  here  described,  par- 
ticular attention  should  be  given  to  the  items  involved  in  the 
problem  and  due  allowance  made  for  varying  conditions  between 
these  examples  and  a  case  under  consideration. 

A  study  of  the  surroundings  and  the  general  building  construc- 
tion should  be  made  in  connection  with  these  notes  and  after 
realizing  the  significance  of  the  features  which  contribute  to 
a  successful  lighting  arrangement,  it  is  quite  possible  that  plans 
drawn  up  with  slight  modifications  from  these  illustrations  and 
notes,  will  insure  far  better  results  than  would  be  the  case  were 
the  question  approached  in  a  more  or  less  haphazard  manner. 


CHAPTER  IX 
IRON  AND  STEEL  MILL  LIGHTING 

90.  General  Items. — The  various  classes  of  work  throughout 
the  buildings  of  iron  and  steel  mills  cover  a  large  number  of  differ- 
ent operations.     Some  of  these  operations  and  locations  may  be 
classed  under  general  heads  as  follows: 

(1)  The  foundry. 

(2)  Open  hearth  furnaces. 

(3)  Machine  shops. 

(4)  Erecting  shops.   . 

(5)  Flanging  shops. 

(6)  Cooling  tables  and  laying  out  floors. 

(7)  Blooming  mills. 

(8)  Loading  sheds. 

(9)  Carpenter  and  pattern  shops. 

(10)  Yards. 

The  work  in  each  of  these  divisions  is  characterized  by  certain 
set  forms,  and  the  problems  connected  with  the  lighting  may  be 
taken  up  perhaps  to  the  best  advantage  if  grouped  under  these 
divisions  of  the  plant. 

Although  practically  every  iron  and  steel  mill  has  its  own  power 
house,  the  lighting  in  these  buildings  has  been  discussed  in  a 
chapter  under  that  subject,  and  is  therefore  not  treated  in  the 
following  pages.  There  are  also  numerous  other  varieties  of  build- 
ings and  work  not  mentioned  in  the  foregoing  list,  most  of  which, 
however,  can  be  included  under  one  or  another  of  the  locations 
mentioned. 

91.  Electrical  Considerations. — A  peculiar  feature  of  the  elec- 
trical equipment  throughout  iron  and  steel  mills  is  the  fact 
that  the  first  application  of  electrical  energy  took  place  years 
before  the  refinements  of  illuminating  engineering  became  recog- 
nized, and  was  originally  connected  with  arc  and  incandescent 
lamps  for  lighting.     This  was  followed  by  the  introduction  of 
electric  motors  in  steel  mill  work,  and  in  this  latter  connection 
the  use  of  the  variable  speed  motor  in  the  past  led  to  an  extended 

125 


126  FACTORY  LIGHTING 

use  of  220-volt  direct- current  circuits  in  many  of  the  mills. 
This  condition  is  somewhat  unique  and  has  produced  certain 
peculiar  features  in  the  light  of  modern  practice.  We  find,  for 
example,  that  as  the  mills  have  increased  in  size  thus  making 
larger  yards  necessary,  the  lighting  of  what  have  now  be- 
come immense  yard  spaces  is  by  means  of  220-volt  direct-cur- 
rent circuits,  with  the  accompanying  excessive  copper  for  feeders. 

Other  difficulties  in  the  selection  of  types  of  lamps  are  brought 
into  evidence  by  the  limitations  of  supply  circuits  in  many 
plants  of  this  kind.  It  is  necessary  to  use  the  1'10-volt  tungsten 
lamp  in  a  multiple  series  arrangement,  that  is,  two  lamps  in 
series  across  220-volt  lines,  in  some  of  the  mills,  and  all  lamps 
of  the  arc  or  mercury  vapor  types  which  possess,  mechanism 
must  in  general  fulfil  the  conditions  for  operation  on  220-volt 
circuits,  wherever  the  plant  is  limited  to  this  one  class  of  circuit. 

Recently,  however,  alternating  current  with  a  frequency  of 
25  cycles  has  been  introduced  in  steel  mill  work,  and  many  of 
the  larger  plants  are  installing  alternating  current,  and  are  con- 
verting only  a  portion  of  the  total  power  for  direct- current  use. 
This  is  an  aid  to  the  lighting  problems,  for  by  a  reference  to 
Table  I  of  Chapter  II  it  will  be  found  that  a  large  number  of  the 
lamps  now  available  may  be  operated  on  one  or  another  of  the 
circuits  just  mentioned.  It  should  be  kept  in  mind  when  con- 
sulting Table  I  that,  while  many  of  the  lamps  are  operative  on 
perhaps  all  of  the  commercial  circuits,  it  may  be  far  better  to 
operate  them  on  some  of  these  than  on  others.  The  table  is 
intended  to  show  what  lamps  are  available  for  the  commercial 
circuits  found  in  practice,  but  it  does  not  show  on  what  circuits 
a  given  type  of  lamp  is  most  advantageously  operated. 

92.  The  Various  Buildings  Involved. — The  typical  iron  and 
steel  mill  building  consists  of  a  large  high-roofed  area  with  dark 
surroundings.  The  areas  to  be  lighted  in  most  of  the  buildings 
are  very  large  when  compared  to  average  factory  conditions, 
and  the  lamps  must  usually  be  in  large  numbers  and  often  in 
large  sizes  so  that  the  required  illumination  may  be  effective  on 
the  work  sometimes  50  ft.  or  more  below  the  lamps. 

The  dark  surroundings  have  a  decided  influence  on  the  amount 
of  light  which  is  effective  on  the  work,  and  in  numerous  cases  vari- 
ous buildings  connected  with  the  steel  plant  will  be  found  where 
the  walls  and  under  side  of  the  roof  are  maintained  a  light  color. 
Thus,  the  reflection  from  walls  and  roof  not  only  aids  the  general 


IRON  AND  STEEL  MILL  LIGHTING 


127 


lighting  effect  but  adds  cheerfulness  to  an  otherwise  gloomy 
interior. 

Nearly  all  steel  mill  buildings  are  of  the  open-girder  con- 
struction with  no  ceiling,  and  hence  the  lamps  must  be  supported 
either  directly  to  the  roof  iron  work,  or  to  the  under  side  of  the 
roof  itself,  if  they  are  to  be  mounted  over-head.  The  buildings 


12g/     Elevation 


-»• 


"i 


H 


Plan 

FIG.  74. — Plan  and  elevation  of  a  typical  foundry  showing  arrangement  of 
flame  carbon  arc  lamps  for  adequate  lighting  effect. 


are  also  nearly  always  equipped  with  a  crane  so  that  the  lamps 
must  usually  be  mounted  directly  above  the  crane. 

93.  General  Requirements. — It  is  difficult  to  outline  specific 
requirements  to  cover  all  cases,  but  the  following  items  are  of 
importance  in  practically  all  the  buildings  involved: 

(1)  For  many  of  the  operations  a  small  amount  of  illumination 
is  sufficient  to  enable  the  workmen  to  get  around  the  building 


128  FACTORY  LIGHTING 

without  accident  risk.     In  general,  however,  a  higher  amount 
of  illumination  is  warranted  than  is  found  in  a  majority  of  cases. 

(2)  Eye  strain  should  be  avoided  by  mounting  the  lamps 
sufficiently  high  to  be  above  the  ordinary  line  of  vision. 

(3)  The  lamps  should  be  operated  from  circuits  which  are 
separate  from  the  motor  circuits,  to  insure  reliable  and  steady 
operation. 

(4)  In  many  cases  the  illumination  must  be  adequate  without 
the  use  of  individual  hand  lamps,  because  of  the  nature  of  the 
work  which  may  prohibit  the  handling  of  an  incandescent  lamp. 
Here  the  illumination  must  be  sufficient  from  over-head  lamps. 

(5)  The  type  of  lamps  and  its  size  should  conform  to  the 
mounting  height  and  to  the  nature  of  the  work. 

(6)  The  yards  should  be  provided  with  fairly  low  uniform 
illumination  in  order  to  aid  in  the  handling  and  transporting  of 
material  by  the  yardmen. 

(7)  Passages  and  walkways  should  be  provided  with  guide 
posts  supporting  lamps,  and  the  many  gauges  connected  with 
steel  mill  operations  require  small  lamps  for  specific  illumination 
on  the  dials. 

Available  lamps  may  now  be  used  for  the  attainment  of  these 
features,  but  for  its  fullest  usefulness,  the  illumination  in  steel 
mills  should  be  of  a  somewhat  higher  standard  than  is  found  at 
present  in  a  large  number  of  the  cases.  The  problems  in  these 
mills  are  often  so  great  as  regards  the  lighting,  that  it  is  some- 
times difficult  to  convince  those  responsible  for  the  expenditures 
of  the  economy  of  such  outlays. 

94.  Peculiar  Importance  of  Over -head  Lighting. — An  observa- 
tion of  conditions  shows  that  much  of  the  work  is  of  large  pro- 
portions thus  requiring  continual  crane  service  in  the  handling  of 
heavy  materials.  Largely  for  this  reason,  in  much  of  the  work 
either  individual  hand  lamps  must  be  used,  or  the  illumination 
must  be  sufficient  from  lamps  over-head.  Hence,  it  is  well  to 
make  the  over-head  lighting  sufficient  even  for  the  large  proc- 
esses and  thus  to  remove  the  need  for  individual  lamps  close  to 
the  work. 

The  comparative  cost  of  the  two  methods  is  relatively  small 
in  difference  when  the  relative  advantages  are  given  due  weight 
in  the  case  of  lamps  well  over-head.  Considerable  work  has  been 
done  in  the  immediate  past  toward  the  introduction  of  this 
scheme  in  steel  mill  work,  but  the  most  important  step  has  been 


IRON  AND  STEEL  MILL  LIGHTING 


129 


the  partial  raising  of  the  standard  of  illumination  as  regards 
quantity.  Before  the  conditions  can  be  pronounced  entirely 
satisfactory,  a  further  step  must  be  taken  in  still  higher  standards 
of  the  quantity  of  light  provided  for  given  classes  of  service. 
For  example,  in  some  of  the  large  machine  shops  heavy  expendi- 
tures have  been  made  to  install  over-head  lamps,  and  the  results 


Elevation 


T 


w 


Pit 


51- 


Elevation 


Pit 


? 


a 


Plan  Plan 

FIG.  75.  FIG.  76. 

FIG.  75. — Plan  and  elevation  of  a  typical  foundry  showing  arrangement 
of  500-watt  tungsten  lamps  for  a  fairly  good  lighting  effect. 

FIG.  76. — Plan  and  elevation  of  a  typical  open-hearth  furnace  building 
showing  a  poor  lighting  arrangement,  with  enclosed  carbon  arc  lamps. 

are  superior  to  former  conditions,  but  still  inadequate  to  permit 
of  accurate  work  without  the  use  of  individual  lamps  close  to 
the  work. 

Another  point  of  importance  is  in  the  providing  of  some  stand- 
ard of  illumination  intensity  for  given  classes   of  work.     In 


130  FACTORY  LIGHTING 

passing  through  the  various  buildings  of  such  plants,  it  will 
sometimes  be  noticed  that  two  similar  classes  of  work  are  fur- 
nished with  entirely  different  intensities.  It  is  recommended, 
therefore,  that  in  studying  the  improvements  required  in  these 
buildings,  attention  be  devoted  to  standards  of  illumination 
which  will  fill  the  requirements  of  each  given  case. 

95.  Adaptation  of  the  Various  Types  of  Lamps.— The  variety 
of  the  buildings  and  the  diverse  nature  of  the  operations,  require 
attention  in  the  selection  of  the  best  type  of  lamp  for  the  purpose 
it  is  to  serve.     The  features  to  be  considered  in  this  connection 
are  discussed  in  Chapter  II  and  are  for  use  in  cases  of  this  kind 
where  it  is  desired  to  adapt  the  lamp  scientifically  to  the  building 
conditions  and  to  the  nature  of  the  work. 

96.  Specific    Locations    Involved.     The    Foundry. — Due    to 
the  dark  surroundings  and  the  presence  of  dust  and  dirt  in  the 
average  foundry,  the  lighting  of  these  departments  is  typical 
of  the  problem  in  the  iron  and  steel  plant.     For  this  reason,  it 
will  be  given  somewhat  more  space  than  would  otherwise  be 
warranted. 

Not  only  must  adequate  light  be  furnished  to  the  moulds,  but 
the  purpose  of  the  light  is  also  to  prevent  stumbling  over  hot 
metal  or  other  accidents  which  may  result  when  the  air  is  filled 
with  steam  and  smoke  at  the  time  of  pouring.  The  surfaces  of 
the  moulds  are  dark,  and  the  dark  walls  and  ceilings  make  it 
necessary  to  provide  more  light  than  would  be  required  if  the 
surroundings  were  light.  It  is  further  important  to  reduce 
shadows  so  that  uneven  places  may  be  detected  on  the  moulds 
when  finishing  the  surfaces  before  pouring,  and  to  have  the  light 
sufficiently  intense  for  the  general  routine  of  foundry  work. 

The  dust,  dirt  and  steam  in  the  air  form  an  obstruction  which 
must  be  penetrated  by  the  light  in  passing  from  the  lamps  to  the 
work,  and  a  deposit  of  dirt  is  apt  to  be  coated  on  the  lamps  which 
causes  the  deterioration  of  the  lamps  in  effectiveness.  This 
makes  it  desirable  to  provide  for  the  deterioration  which  will 
result  between  cleaning  intervals  by  the  providing  of  a  higher 
intensity  of  light  at  the  start  than  would  otherwise  be  thought 
necessary.  It  also  makes  it  desirable  to  use  a  type  of  lamp  which 
will  not  be  rapidly  affected  by  the  dirt  deposits. 

Fig.  74  shows  the  design  for  a  foundry  where  lamps  of  the  flame 
carbon  arc  type  are  indicated.  The  yellow  light  from  these 
lamps  as  well  as  the  light  of  the  mercury  vapor  lamp  is  pene- 


IRON  AND  STEEL  MILL  LIGHTING 


131 


trating  in  an  exceptional  degree  and  thus  tends  to  illuminate  the 
dark  surfaces  sufficiently.  The  diagram  shows  that  the  lamps 
are  mounted  rather  close  to  the  moulds  because  of  the  low-roof 
supports,  but  this  is  rather  an  advantage  in  the  foundry  if  not 


|   ! 

i  * 
P. 

V 

[A 

^^^^ 

jrnace^ 

^^^ 

Elevation    | 

!J 
p 

\ 

-»)12 

^- 

«  — 

5    "<: 
$    t 

*           1 

*• 

'urnace 

Girder 

Line/ 

-« 

|   1 

5 

t 

- 

I, 

$        ** 

Elevation 


131-30' 4-— 

*  « 


Girder  Line' 


K 


H 


Plan  Plan 

FIG.  77.  FIG.  78. 

FIG.  77. — Plan  and  elevation  of  a  typical  open-hearth  furnace  building 
showing  an  improved  lighting  arrangement.  Compare  with  Fig.  76.  This 
system  designed  for  use  of  long  burning  flame  carbon  arc  lamps. 

FIG.  78. — Plan  and  elevation  of  typical  steel  mill  machine  shop  showing 
arrangement  of  enclosed  carbon  arc  lamps. 

carried  to  an  extreme  by  mounting  them  so  low  as  to  produce 
glare. 

Fig.  75  shows  an  installation  of  smaller  lamps,  namely,  the 
500-watt  tungsten  type.  Although  the  dust  and  dirt  are  apt 
to  cause  a  more  rapid  deterioration  with  this  type  of  lamp,  it 


132 


FACTORY  LIGHTING 


may  be  used  in  some  cases  where  the  dust  does  not  occur  in  such 
large  quantities.  It  will  be  noted  that  the  size  of  lamp  in  the 
preceding  case  is  somewhat  larger  than  would  be  thought  desira- 
ble from  the  tables  in  Chapter  II.  This  exception  to  the  general 
standard  is  perhaps  warranted,  however,  due  to  the  extreme  con- 
ditions of  the  surroundings  which 
are  usually  darker  than  in  most  of 
the  other  buildings. 

Open-hearth  Furnaces.— The 
amount  of  light  required  for  these 
buildings  is  small  in  comparison  to 
other  locations  as  the  light  from 
the  furnaces  aids  the  workmen  in 
getting  about.  A  small  amount  of 
general  lighting  is  warranted,  how- 
ever, and  is  necessary  for  safety  and 
for  effective  work. 

Fig.  76  shows  a  typical  installa- 
tion where  the  light  is  inadequate, 
while  in  Fig.  77  another  plan  for 
lighting  such  a  building  is  shown. 
In  the  second  illustration  the  num- 
ber and  type  of  lamps  is  calculated 
to  give  the  desirable  quantity  of 
light  to  facilitate  the  work  about 
the  furnaces.  The  light  from  the 
furnaces  is  intermittent  and  hence 
should  not  be  relied  upon  as  the 
main  source  of  illumination,  and 
further  the  spaces  back  of  the  fur- 
naces require  light  specially  when 
loading  is  carried  on  there. 

Machine  Shops. — The  questions 
of  machine-shop  lighting  have  been 
covered  in  a  former  chapter.  Some 
of  the  shops  about  steel  mills,  how- 
ever, are  unusually  large  and  Fig.  78  gives  some  idea  of  such 
a  space  with  a  fairly  low  ceiling  where  enclosed  carbon  arc 
lamps  are  used  to  advantage.  Fig.  79  shows  a  shop  with 
high  ceiling  or  girder  line  where  large  lamps  are  indicated. 
The  arrangement  of  lamps  in  the  latter  illustration  apparently 


Elevation 


X  « 

56'6»  -- - 

Girder  Line  / 


Plan 

FIG.  79. — Plan  and  eleva- 
tion of  typical  steel  mill 
machine  shop  showing  ar- 
rangement of  700  candle-power 
mercury  vapor  lamps  for  high 
mounting. 


IRON  AND  STEEL  MILL  LIGHTING  133 

was  calculated  to  furnish  enough  light  from  over-head  to  make 
individual  lamps  unnecessary,  the  intensity  on  the  work  being 
about  2  foot-candles,  although  with  an  intensity  of  this  value 
individual  lamps  are  actually  required  for  many  machining 
operations. 

Machine  shops  about  steel  mills  are  to  be  found  where  intensi- 
ties as  low  as  8/10  foot-candle  are  erroneously  considered  sufficient 
for  general  lighting  purposes,  but  in  practically  all  such  cases 


FIG.  80. — Reproduced  from  a  photograph  taken  at  night  under  the  arti- 
ficial light  in  a  typical  steel  mill  machine  shop.  Note  the  excellent  dis- 
tribution of  the  light  produced  by  700  candle-power  mercury  vapor  lamps 
in  this  location. 

individual  lamps  are  placed  close  to  the  work.  If  the  individual 
lamps  are  to  be  eliminated,  therefore,  it  is  necessary  to  provide 
higher  intensities  from  the  over-head  lamps.  Fig.  80  illustrates 
the  excellence  which  may  be  attained  by  a  well-designed  installa- 
tion of  shop  lighting  in  a  steel  mill. 

Erecting  Shops. — The  buildings  used  for  erecting  large  machines 
are  often  of  very  large  proportions  with  high  roof  clearance. 
Distances  of  70  ft.  between  floor  and  girder  line  are  to  be  found, 


134 


FACTORY  LIGHTING 


Elevation 


and  the  supplying  of  sufficient  illumination  to  the  work  from 
lamps  at  this  height  is  difficult.  Fig.  81  shows  such  a  space 
where  mercury  vapor  lamps  of  about  700  candle-power  each 
are  employed.  These  lamps  are  mounted  70  ft.  above  the  floor 
and  furnish  an  intensity  of  about  8/10  foot-candle  on  the  work 

near  the  floor.  This  quantity  of 
illumination  is  fairly  adequate 
but  hardly  sufficient  for  contin- 
uous work  and  close  application. 
Somewhat  higher  intensities  are 
therefore  recommended  for  this 
class  of  work  as  an  economy  to 
the  operations. 

Flanging  Shops. — The  work  of 
flanging  boiler  heads  and  other 
shapes  is  carried  on  while  the 
metal  is  at  a  red  heat,  and  the 
artificial  light  required  is  there- 
fore correspondingly  reduced.  In 
handling  this  material,  however, 
after  it  has  cooled,  a  low  amount 
of  general  illumination  is  re- 
quired at  night,  somewhat  higher 
than  is  to  be  found  in  the  average 
building  of  this  kind.  Fig.  82 
shows  a  diagram  of  a  typical 
building  where  the  lamps  are  in- 
dicated. The  average  intensity 
in  this  location  was  found  by 
measurement  to  be  very  low  and 
entirely  inadequate  for  the  quick 
handling  of  the  cold  metal  at 
night.  Fig.  83  shows  an  ar- 
rangement of  lamps  calculated 
to  be  sufficient  for  the  work, 
the  intensity  in  the  latter  case  amounting  to  between  1  and  2 
foot-candles. 

Cooling  Tables  and  Laying  out  Floors. — The  cooling  tables 
for  large  metal  plates  are  generally  used  for  laying  out  the  work 
as  well.  As  the  metal  cools  the  plates  are  tipped  on  edge  for 
inspection  and  it  is  at  this  point  that  artificial  light  is  most  impor- 


Girder  Line' 


Plan 

FIG.  81. — Plan  and  elevation  of 
typical  erecting  shop  in  a  steel 
mill  showing  arrangement  of  700 
candle-power  mercury  vapor  lamps 
for  very  high  mounting. 


IRON  AND  STEEL  MILL  LIGHTING 


135 


tant.  It  has  been  found  that  the  mercury  vapor  lamp  is  well 
suited  for  this  inspection  work  with  some  classes  of  material. 
In  other  cases  where  the  material  is  different  the  opinion  of  some 
operators  is  that  the  light  from  the  mercury  vapor  lamp  does 
not  bring  out  certain  defects  in  the  metal  as  well  as  a  more  yel- 
low light.  For  these  reasons  no  definite  rules  can  be  stated 


Elevation 


K 


Plan 

FIG.  82. — Plan  and  elevation  of  typical  steel  mill  flanging  shop  showing 
very  poor  arrangement  of  lamps.  The  lamps  of  700  candle-power  are  much 
too  far  apart. 


as  to  the  quality  of  light  best  suited  for  the  inspection  of  all 
sheet  metal,  but  the  intensity  of  the  light  for  this  operation 
should  equal  from  1  to  2  foot-candles  to  facilitate  accurate 
inspection. 

After  the  plates  have  been  inspected,  the  various  shapes  are 
chalked  out  while  the  metal  is  in  a  horizontal  position,  and  at 


136 


FACTORY  LIGHTING 


this  time  the  lighting  must  be  fairly  intense,  both  on  dark  days 
and  at  night.  Fig.  84  shows  one  location  where  the  lamps  are 
indicated.  In  this  particular  case  the  lighting  shown  is  very 
much  superior  to  the  former  conditions  with  an  older  system, 
but  observation  and  test  seem  to  indicate  that  the  light  is  still 
inadequate  for  rapid,  accurate  and  continuous  work.  The 


Girder  Line 


«- 


B— 


Plan 

FIG.  83. — Plan  and  elevation  of  typical  steel  mill  flanging  shop  showing 
improved  arrangement  of  700  candle-power  lamps.  Compare  with  Fig.  82 
and  note  the  closer  spacing  in  this  improved  scheme. 

intensity  found  here  amounts  to  about  1  foot-candle,  while 
about  1  1/2  foot-candles  should  be  the  average  with  the  mercury 
vapor  lamps  here  used. 

Blooming  Mills. — The  work  in  the  blooming  mill  is  usually 
carried  on  with  the  metal  at  a  red  heat,  and  while  the  metal  is 
passing  through  the  rolls,  practically  no  artificial  light  is  required. 


IRON  AND  STEEL  MILL  LIGHTING 


137 


Since  the  work  is  intermittent,  however,  the  illumination  avail- 
able from  the  lamps  should  be  sufficient  not  only  for  the  regular 
work  but  for  repairs.  Fig.  85  shows  a  portion  of  a  blooming 
mill  where  the  lamps  are  located  near  the  walls,  hence  the  light 
is  very  poor  in  the  central  portions  of  the  building.  An  improved 
scheme  is  shown  in  Fig.  86  where  the  light  by  a  higher  mount- 


FIG.  84. — Plan  and  elevation  of  typical  steel  mill  cooling  tables  and  laying 
out  floor  showing  arrangement  of  800  candle-power  mercury  vapor  lamps. 
The  work  of  marking  the  plates  is  carried  on  directly  below  the  lamps  shown 
in  this  diagram.  . 

ing  is  distributed  more  uniformly  over  the  floor  space.  If  the 
control  circuits  are  arranged  properly  the  lamps  in  this  latter  plan 
may  be  used  economically  by  turning  off  the  units  not  required. 
Loading  Sheds. — Here  the  metal  is  handled  in  a  cold  state, 
and  the  work  must  usually  be  done  with  dispatch  in  loading  cars. 


138 


FACTORY  LIGHTING 


The  entire  floor  space  should  thus  be  lighted  by  lamps  so  con- 
trolled that  when  the  work  is  grouped  at  one  portion  of  the  build- 
ing only,  those  units  not  required  may  be  turned  off.  It  is  better 
to  have  the  spaces  in  use  lighted  adequately  when  required,  than 
to  have  all  the  lamps  turned  on  at  all  times  and  have  so  few 
installed  that  the  lighting  at  no  point  is  sufficient.  Fig.  87 


f 


Elevation 


Elevation 


~? 


-81— 


Girder  Line- 
X 


X 


Incandescent' 
Cluster 


X 


X 


Plan  Plan 

FIG.  85.  FIG.  8J. 

FIG.  85. — Plan  and  elevation  of  typical  steel  mill  blooming  department 
showing  poor  arrangement  of  enclosed  carbon  arc  lamps  and  incandescent 
lamp  clusters.  The  arc  lamps  are  too  close  to  the  walls  and  all  the  lamps 
are  so  low  as  to  cause  an  objectionable  glare  for  the  workmen. 

FIG.  86. — Plan  and  elevation  of  typical  steel  mill  blooming  department 
same  as  shown  in  Fig.  85,  showing  improved  arrangement  of  lamps  making 
use  of  the  flame  carbon  arc  type.  Note  the  more  symmetrical  spacing 
and  the  greater  distance  between  lamps  and  walls  thus  distributing  the  light 
more  uniformly  over  the  floor  area.  Compare  with  Fig.  85. 

shows  a  loading  shed  where  the  lamps  furnish  about  1  1/2  foot- 
candles.  This  intensity  is  in  general  sufficient,  unless  the  use 
of  very  large  lamps  in  small  numbers  causes  marked  shadows, 
where  the  effect  may  be  much  improved  by  increasing  the  number 
of  lamps,  and  possibly  using  a  smaller  size  of  unit. 

Pattern  and  Carpenter  Shops. — The  typical  shop  under  this 


IRON  AND  STEEL  MILL  LIGHTING  139 

head  consists  of  a  long,  narrow  building  with  comparatively  low 
ceiling.  The  surfaces  of  the  wood  are  usually  light  in  color  and 
the  surroundings  brighter  than  in  many  of  the  other  locations. 
This  feature  is  an  aid  to  the  artificial  light.  Fig.  88  shows  an 
arrangement  of  500-watt  tungsten  lamps  in  such  a  building, 
where  the  illumination  intensity  is  sufficient  and  the  distribution 
of  the  light  uniform. 

Yards. — The  lighting  here  should  be  sufficient  to  reduce 
accidents,  and  to  help  in  the  dispatching  of  cars  loaded  with 
material  between  the  buildings.  There  is  much  night  work  in 
most  steel  plants  and  for  this  reason  the  arrangement  of  the  lamps 
throughout  the  yard  spaces  should  be  given  due  attention.  In 
general,  a  diagram  of  the  yards  will  be  a  help,  since  on  this 
the  poles  may  be  arranged  systematically  to  secure  general 
lighting  with  particular  reference  to  the  reduction  of  shadows  in 
dangerous  places.  Fig.  89  shows  a  diagram  of  the  lamp  arrange- 
ment in  a  small  yard  where  the  units  are  planned  to  illuminate 
entrances  to  the  buildings  and  also  important  points  on  the  tracks 
and  where  material  is  stored. 

97.  Other  Items. — The  foregoing  illustrations  as  well  as  the 
data  in  Table  XII  indicate  in  a  general  way  the  work  connected 
with  the  lighting  in  and  around  steel  plants,  and  in  this  manner 
the  idea  has  been  emphasized  that  individual  treatment  must  be 
given  to  a  large  number  of  the  cases  that  arise. 

The  presence  of  hot  metal  in  some  of  the  buildings  is  some- 
times used  as  an  excuse  for  not  installing  many  lamps,  but  the 
light  from  this  source  is  intermittent  and  the  contrast  is  made 
the  greater  by  this  cause,  and  adequate  artificial  light  should 
be  provided  for  the  dark  intervals. 

Much  attention  has  been  directed  during  recent  years  to  acci- 
dent reduction  by  preventive  measures,  as  in  the  surrounding  of 
dangerous  moving  machine  parts  with  guards.  Artificial  light 
will  likewise  do  much  to  reduce  accidents  and  this  feature  is  one 
of  the  very  important  considerations  where  the  lighting  of  a  given 
space  is  in  question. 

The  maintenance  of  the  lamps  is  very  important  and  this 
subject  has  been  discussed  in  the  chapter  under  that  head.  One 
point  of  particular  interest,  however,  is  a  tendency  to  neglect 
the  upkeep  of  lamps  not  calling  for  regular  attention.  That  is, 
the  tungsten  and  the  mercury  vapor  lamps  do  not  require  trim- 
ming like  the  arc  lamp,  but  they  should  be  maintained  with  the 


Ill 

ill! 


i 


1    I 


i?  15 
J  t 


.]  !          i 


!1!1     I 


g       1 1 ill I 1 

1 


l*i: 


Su5M-<eo 
«CO-HT)« 


III 


lii 


II. 


lip 


I! 


53  S  2  2 


I 


cocococo        co  oo  co     •  co  co  co 


S jl  Jff  !§SS j 

llllllllll 

s  bS  b^iig  s  s  s  >> 


>  2  3  « 

III! 

ssss 


ill 


uuguS£u 


in 

IN 

Ii| 

^ 


l-i 


11   ^    :' 

•II  :  : 
Us  ; 


II: 


j 


{!  I   Jf l!    I 

ill       ill]      1 

E2^     £o(£S     ^i 


ill 
fc 


I  ^"2 


I! 


fJ 

lll 


140 


IRON  AND  STEEL  MILL  LIGHTING 


141 


same  care.  An  observation  of  some  installations  of  the  former 
types  of  lamps  shows  that  sometimes  many  of  the  lamps  are  out 
of  service  and  apparently  no  attention  is  given  the  matter. 

One  argument  advanced  by  a  practical  man  has  been  that  the 
use  of  a  large  number  of   medium-sized  lamps  makes  possible 


Elevation 


XX 
XX 

XX  XX 

XX  XX 

XX  X* 

XX  J3 

XX 


XX 


Plan  Plan 

FIG.  87.  FIG.  88. 

FIG.  87. — Plan  and  elevation  of  typical  steel  mill  loading  shed  showing 
arrangement  of  flame  carbon  arc  lamps. 

FIG.  88. — Plan  and  elevation  of  typical  pattern  shop  showing  an  arrange- 
ment of  500-watt  tungsten  lamps. 


one  or  another  of  the  lamps  going  out  without  affecting  the 
service  to  any  great  extent.  If  this  argument  were  carried  to 
the  extreme,  one  might  conclude  that  one-eighth  or  one-fourth 
of  the  lamps  out  of  service  would  not  materially  affect  the 
light  if  the  bad  lamps  were  uniformly  distributed  through  the 


142 


FACTORY  LIGHTING 


system.     If  this  were  true,  they  might  have  been  left  out  of  the 
original  installation. 

The  state  of  affairs  amounts  to  this,  that  while  a  few  lamps 
in  a  distributed  system  may  be  out  here  and  there  without 
affecting  the  uniformity  of  the  illumination  to  any  great  extent, 
the  resulting  intensity  of  the  illumination  is  reduced  in  a  definite 
manner,  and  if  neglect  of  the  renewal  and  repair  of  the  lamps  is 
persisted  in,  the  old  conditions  of  inadequate  lighting  are  apt 


Shop 


—212- -*4« 200- 

W 


w 


Plan 


FIG.  89. — Plan  of  a  typical  steel  mill  yard  showing  suggested  arrangement 
of  flame  carbon  arc  lamps. 

to  become  permanent.  It  is  thus  apparent  that  to  have  lamps 
which  do  not  require  regular  trimming  as  does  the  arc  type,  while 
a  seeming  advantage  at  the  outset,  may  prove  to  be  a  disadvan- 
tage to  the  best  operation  of  the  lighting  equipment  if  it  encour- 
ages neglect  in  the  regular  maintenance. 

98.  Economy  of  Superior  Lighting  Facilities. — In  a  former 
paragraph  it  was  shown  that  the  economy  of  good  lighting  may 
be  reduced  to  the  wages  saved  through  the  facilities  it  affords. 
In  the  operations  of  iron  and  steel  mills,  it  is  often  found  that  the 
number  of  workmen  for  a  given  floor  area  is  small  in  comparison 


IRON  AND  STEEL  MILL  LIGHTING  143 

to  the  conditions  in  ordinary  factory  buildings.  It  is  perhaps 
a  better  scheme,  therefore,  to  base  such  conclusions  here  on  the 
advantages  of  light  to  an  increase  in  the  tonnage  output.  This 
feature  is  evident  in  those  cases  where  the  merits  of  various 
divisions  of  the  mill  are  based  on  the  tonnage  scheme.  Thus,  if 
the  tonnage  output  in  a  given  department  is  increased  by  a 
certain  percentage  by  improved  lighting,  the  facilities  afforded  by 
the  lighting  are  an  asset  to  the  equipment  of  the  department. 

Economy  also  results  if  defective  work  is  reduced  by  better 
lighting.  On  the  laying-out  floor,  for  example,  if  a  metal  plate 
is  defective,  but  due  to  the  poor  lighting  it  is  passed  as  good 
material,  the  plate  may  go  through  a  considerable  number  of 
subsequent  operations  before  a  final  inspection  indicates  the 
defect.  The  loss  of  time  on  this  work  includes  not  only  that  of 
the  original  inspector,  but  also  that  of  the  workmen  on  subse- 
quent operations,  and  is  a  loss  to  the  plant  chargeable  to  insuffi- 
cient OT  poorly  distributed  light  for  the  original  inspector. 

Hence,  it  is  an  advantage  and  an  asset  to  provide  not  merely 
some  artificial  light,  but  sufficient  illumination  to  be  effective 
in  securing  the  largest  tonnage  from  a  given  working  force  by 
facilitating  the  regular  operations  and  preventing  accidents 
and  delays,  and  defective  workmanship.  The  electrical  depart- 
ments should  endeavor  to  inform  those  responsible  for  the  ex- 
penditures for  electrical  equipment  as  to  the  merits  of  im- 
proved lighting,  and  to  give  regard  to  the  relations  of  sufficient 
light  to  the  large  operations  which  it  continually  influences.1 

1  See  paper  by  the  author  on  "Modern  Illumination  in  the  Iron  and 
Steel  Industry,"  Transactions  Association  of  Iron  and  Steel  Electrical 
Engineers,  October,  1912. 


CHAPTER  X 
MACHINE  TOOL  LIGHTING 

99.  Importance  of  Adequate  Light  on  the  Machine  Tool. — As 
stated  in  an  earlier  paragraph,  the  term  light  refers  to  the  source 
or  the  lamp,  while  the  term  illumination  refers  to  the  effect 
produced  by  the  lamp  on  the  work  or  object  to  be  lighted.     The 
items  involved  in  the  illumination  of  the  work  in  a  machine  tool 
include  some  of  the  features  of  the  light  as  well  as  certain  ele- 
ments in  the  illumination. 

The  best  scheme  for  lighting  in  the  factory  is  probably  by 
the  over-head  system  where  the  lamps  are  separate  from  the 
individual  tools,  and  where  the  illumination  is  sufficient  in  both 
quantity  and  in  direction  to  make  the  work  easily  visible.  In 
this  way  the  workmen  are  unhampered  by  a  hand  lamp  which 
is  apt  to  be  in  the  way,  and  the  surroundings  as  well  as  the  small 
space  on  the  work,  are  thus  properly  illuminated.  If,  on  the 
other  hand,  the  lamp  is  directly  over  and  close  to  the  work,  the 
operations  are  somewhat  complicated  by  the  relatively  dark 
spaces  outside  the  small  portion  of  the  work  furnished  with 
plenty  of  light. 

To  properly  light  the  machine  tool  the  over-head  system 
should  first  be  considered,  and  if  it  is  necessary  to  employ  an 
individual  lamp  in  addition  to  the  light  supplied  from  over-head, 
a  study  should  be  made  of  the  best  manner  in  which  to  mount 
the  lamp  on  the  machine  and  the  means  for  concentrating  the 
light  from  the  individual  lamp  at  the  point  of  operation.  Finally 
the  cost  relations  should  be  given  due  weight  as  showing  the  neces- 
sity for  heeding  each  separate  item  involved. 

100.  Cases   Provided   for   by    Over-head   Lamps. — As   just 
stated,  the  lighting  of  the  machine  tool  should  always  be  through 
the  medium  of  a  lamp  or  lamps  separate  and  apart  from  the 
machine  wherever  possible.     The  side  light  is  a  most  important 
item,  and  it  has  been  found  that  in  many  cases  the  only  special 
feature  required  for  making  the  lighting  from  over-head  lamps 
sufficient  is  to  intensify  the  side  light  rather  than  the  vertically 
downward  component.     The  absence  of  this  side  component 

144 


MACHINE  TOOL  LIGHTING 


145 


10 


146 


FACTORY  LIGHTING 


is  often  the  reason  why  the  operator  of  a  machine  tool  considers 
an  individual  lamp  necessary. 

Cases  are  recorded  where  machine  tools  formerly  lighted  by 
individual  lamps  have  been  provided  with  better  illumination 
from  over-head  lamps  slightly  lowered  from  the  ceiling  and  pro- 
vided with  suitable  reflectors. 

In  many  factory  sections  for  every  square  foot  occupied  by 
a  machine  tool  there  is  a  corresponding  area  used  for  the  storage 
of  materials  and  supplies  needed  for  the  work.  Hence,  if  the 


Machine  Tool 


FIG.  92. — Special  bracket  designed  for  individual  machine  tool  lamp. 

machine  tool  can  be  lighted  satisfactorily  by  over-head  lamps, 
the  surrounding  space  receives  a  corresponding  advantage. 
The  over-head  lamps  in  a  case  of  this  kind  perve  the  double 
purpose  of  lighting  the  machine  tool  and  the  adjoining  space 
as  well.  Fig.  90  shows  a  machine  tool  poorly  lighted  by  a  hand 
lamp  close  to  the  work,  while  Fig.  91  shows  the  same  machine 
illuminated  by  tungsten  lamps  which  have  been  slightly  lowered 
from  the  ceiling  to  a  height  depending  on  the  size  of  the  machine. 
101.  Points  on  the  Mounting  of  Individual  Lamps. — In  many 
machining  operations  the  work  must  be  viewed  from  below  as 
well  as  from  the  side  and  from  above,  as  in  the  case  of  some 


MACHINE  TOOL  LIGHTING 


147 


milling  machines.  Experiments  have  been  conducted  for  the 
purpose  of  producing  sufficiently  intense  side  light  in  such  cases 
from  over-head  lamps,  but  sometimes  no  amount  of  light  from 
over-head  will  reach  the  important  places. 

To  overcome  this  feature  brackets  may  be  mounted  on  the 
machine  tools  somewhat  after  the  illustration  in  Fig.  92,  and 
in  this  way  the  lamp  may  be  moved  through  a  considerable 
range  and  in  various  directions  so  that  the  workman  may  adjust 
the  lamp  to  suit  his  requirements. 


FIG.  93. — Special  support  designed  for  lamp  on  a  boring  mill. 

In  large  boring  mills  individual  lamps  are  also  sometimes  very 
necessary,  specially  when  they  are  placed  in  high  aisles  with  the 
overhead  lamps  so  far  away  that  it  is  impossible  to  produce  the 
needed  amount  of  side  light.  Fig.  93  shows  one  scheme  for 
mounting  individual  lamps  on  these  machines.  The  lamp  is 
suspended  on  a  swinging  arm,  which  is  attached  either  to  the 
side  wall  or  to  the  vertical  portion  of  the  machine  itself.  Large 
machines  require  mild  general  illumination  and  also  high  inten- 
sity at  the  cutting  point. 

Concentrating  the  Light  Where  Required. — The  average  work- 
man has  some  idea  of  the  importance  of  shielding  his  eyes  from 
the  light  of  a  bare  lamp,  because  he  often  surrounds  the  bare 
lamp  with  a  cardboard  or  metal  cone,  which  while  shielding  the 


148 


FACTORY  LIGHTING 


eyes  does  not  add  anything  to  the  net  efficiency  of  the  lamp. 
Hence,  the  light  should  not  only  be  cut  off  from  the  eyes  but 
directed  to  the  object  which  must  be  visible  for  the  workman. 

Fig.  94  shows  the  approximate  distribution  of  light  about  a 
bare  incandescent  lamp,  not  provided  with  a  shade  or  reflector. 
Here  much  of  the  light  is  wasted  in  directions  not  useful  to  the 
work,  and  when  the  work  is  viewed  from  behind  the  lamp, 
almost  as  much  light  enters  the  eye  as  is  effective  on  the  work 
itself. 


FIG.  94. — Approximate  distribution  curve  of  a  bare  or  unprotected  carbon 
filament  lamp.  Much  light  is  wasted  in  useless  directions.  Note  the  direc- 
tion of  the  light  rays  as  related  to  the  milling  cutter  on  the  right. 

Fig.  95  shows  the  approximate  distribution  of  light  about  a 
lamp  which  is  equipped  with  a  dark  metal  shield.  This  shows 
that  the  eye  is  protected  from  the  glare,  but  the  amount  of  light 
on  the  work  is  about  the  same  as  before,  that  is,  the  improvement 
is  only  a  partial  one. 

Fig.  96  shows  the  approximate  distribution  about  a  lamp 
equipped  with  a  suitable  reflector,  and  by  comparing  this  illus- 
tration with  the  two  preceding,  it  is  apparent  that  here  the  eye 
is  protected  and  that  most  of  the  light  is  directed  to  the  point 
required  jDy  means  of  the  reflecting  surface  on  the  inside  of  the 
reflector. 


MACHINE  TOOL  LIGHTING 


149 


Therefore,  if  the  illumination  was  sufficient  without  a  reflector 
in  the  first  case,  a  smaller  lamp  might  be  used  when  equipped 
with  a  reflector  for  directing  the  bulk  of  the  light  to  the  cutting 
point.  On  the  other  hand,  if  the  light  was  insufficient  with  the 
bare  lamp,  it  will  likely  be  adequate  with  the  addition  of  a 
reflector. 

Figs.  97  and  98  are  two  views  of  the  same  machine.  A 
lamp  without  a  reflector  is  used  in  the  first  case  and  the  glare 


FIG.  95. — Approximate  distribution  curve  of  a  carbon  filament  lamp 
with  improvised  metal  shade.  Much  light  is  wasted  by  absorption  on 
the  inside  of  the  shade  and  only  a  small  proportion  of  the  available  light 
reaches  the  cutter  to  the  right. 


is  shown  by  the  illustration.  In  the  second  case  the  lamp  is 
equipped  with  a  reflector  and  the  effect  is  shown  by  the  reduced 
glare  on  the  photographic  reproduction. 

102.  Cost  Relations  of  Artificial  Light  and  Machine  Tool 
Operation. — The  many  improvements  to  machine  tools  include 
mechanical  features  as  well  as  the  more  efficient  methods  of 
driving.  There  are  two  other  items  which  are  essential  if  the 
greatest  benefit  is  to  be  derived  from  these  improvements, 


150 


FACTORY  LIGHTING 


namely,  the  efficiency  of  the  man  who  operates  the  machine,  and 
the  surroundings  of  the  man,  which  influence  him  in  his  work. 

Therefore,  the  efficiency  of  the  operator  may  be  the  controlling 
element  in  the  production  resulting  from  a  given  machine  tool. 
The  artificial  light  affects  the  efficiency  of  the  operator  contrib- 
uting either  to  his  success  or  failure,  depending  on  whether  it 
is  adequate  or  inadequate  on  dark  days  and  at  night.  The 
development  of  machine  tools  has  generally  overlooked  the  devel- 


FIG.  96. — Approximate  distribution  curve  of  a  carbon  filament  lamp 
equipped  with  a  well-designed  reflecting  shade.  Most  of  the  available 
light  is  directed  to  the  cutter  at  the  right. 

opment  of  proper  lighting  features  as  a  distinct  portion  of  the 
machine  itself,  this  item  in  the  main  being  left  to  the  judgment 
of  the  one  who  installs  it  and  has  its  operation  under  control. 

Fig.  99  and  Table  XIII  show  the  items  chargeable  against  a 
particular  machine  tool1.  It  will  be  seen  that  the  cost  for  energy 
and  maintenance  of  the  lamp  is  the  smallest  item.  These 
charges  may  be  larger  or  smaller  than  the  average,  but  are  selected 

1  From  article  by  A.  G.  Popcke  in  Electric  Journal,  Dec.,  1909,  p.  760. 


MACHINE  TOOL  LIGHTING 


151 


152  FACTORY  LIGHTING 

from  a  typical  case,  and  the  main  point  to  note  is  that  the  lighting 
is  almost  a  negligible  expense  in  comparison  to  the  other  charges, 
although  it  may  be  the  cause  for  the  failure  of  the  workman  on  a 
given  piece  of  material.  In  one  factory  section,  the  cost  of  energy 
and  maintenance  per  individual  lamp  amounted  to  25  cents  per 
month.  The  operator  who  depends  on  this  lamp  may  receive 
$3.00  per  day,  hence  the  cost  of  the  lamp  is  equal  to  the  wages 
for  two  minutes  per  day.  A  workman  can  easily  lose  that 
amount  of  time  and  far  more  if  he  is  handicapped  in  every  motion 
by  an  insufficiency  of  light  at  certain  portions  of  the  day,  or  at 
night,  and  when  losses  due  to  defective  work  are  added  to  the 
losses  of  time,  they  may  greatly  exceed  the  cost  for  the  best 
available  light. 

TABLE  XIII. — CHARGES  PER  HOUR  AGAINST  A  TYPICAL  MACHINE  TOOL 

Variable  charges $1 . 100 

Salaries. . 600 

Wages  of  operator 300 

Interest 150 

Depreciation 150 

Fixed  charges 060 

Power,  for  motor  drive 020 

Power,  for  individual  lamp 001 


Total.... $2.381 

Fig.  64  shows  these  relations  in  a  more  definite  manner  for 
various  conditions,  and  therefore  it  may  be  stated  that  while 
the  light  is  one  of  the  smallest  items  connected  with  the  operation 
of  a  machine  tool,  it  is  in  reality  more  important  in  its  results 
than  some  other  items. 

103.  Physical  Size  of  the  Individual  Lamp. — The  individual 
lamp  should  be  as  small  as  is  consistent  with  good  practice  in 
the  handling  of  the  lamps.     Evidently  the  size  of  the  lamp  may 
be  reduced  if  a  reflector  is  used  and  by  the  reduction  of  the  size 
of  the  entire  unit,  it  will  be  less  likely  to  be  in  the  way  when 
handled  by  the  operator,  and  it  can  thus  be  placed  closer  to  the 
point  of  work  than  otherwise. 

104.  Extension  Lines.— In  some  cases  the  lamps  cannot  con- 
veniently be  attached  to  the  machinery  but  must  be  used  in  the 
form  of  extension  lines.     If  the  number  of  these  flexible  lines  is 
very  great,  the  maintenance  is  apt  to  be  large  unless  special  care 
is  taken  in  the  makeup  of  the  line. 


MACHINE  TOOL  LIGHTING 


153 


The  usual  form  is  a  length  of  flexible  lamp  cord  to  which  a 
wood  handle  and  a  socket  are  attached  at  one  end  and  an  attach- 
ment plug  to  the  other.  Here  the  cord  is  frequently  mashed 
or  cut,  thus  wearing  off  the  insulation,  the  plug  may  be  dropped 
and  broken,  and  the  unprotected  socket  is  often  left  lying  on  the 
floor  and  is  stepped  on  and  broken.  The  lamp  guard  usually 
employed  is  weak  in  construction  and  may  be  mashed  if  stepped 
on.  A  study  of  these  weak  points  resulted  in  the  design  of  an 
extension  line  made  up  of  flexible  deck  cable  to  one  end  of  which 


Variable  Charges 
Salaries 
Wages 
Interest 
Depreciation. 
Fixed  Charges 
Power 
Individual  Lamp 


20 


40 


Cents 


bO 


100 


FIG.  99. — Charges  per  hour  against  a  typical  machine  tool,  showing  the 
comparative  insignificance  of  the  lighting  cost  in  terms  of  the  total. 


is  attached  a  special  wood  guard  into  which  the  socket  is  fastened, 
and  to  which  the  lamp  guard  is  also  fastened.  This  combination 
socket  and  lamp  guard  is  able  to  withstand  a  great  deal  of  wear 
and  tear,  and  the  metal  part  of  the  guard  is  strong  enough  to 
bear  the  weight  of  a  man  on  account  of  its  reinforcing  ribs.  A 
wood  handle  forms  a  part  of  the  whole  and  is  so  proportioned 
that  a  workman  can  easily  manipulate  the  line  to  suit  his 
requirements . 

At  the  other  end  of  the  line  a  wood  attachment  is  screwed  to 
the  plug  connection  so  that  there  is  no  cause  for  the  wire  to  be 
broken  off  where  it  enters  either  the  plug  or  the  socket.  Fig. 
100  shows  the  fittings  for  this  form  of  line,  which  although  some- 
what more  expensive  than  the  ordinary  kind,  will  wear  several 
times  as  long,  thus  proving  an  economy  in  the  end. 

105.  Shadow  Contrasts. — Sometimes  the  individual  hand  lamp 
is  needed  to  help  in  the  making  of  delicate  fittings  by  the  shadow 
contrast  between  the  respective  edges  of  the  material.  This 
particular  effect  can  hardly  be  secured  in  any  other  way  than 
by  the  use  of  a  lamp  in  the  hand  of  the  workman.  This  applies 


154 


FACTORY  LIGHTING 


to  the  work  on  dies  and  to  some  assembly  operations.     Here  of 
course  the  hand  lamp  is  an  aid  and  not  a  hindrance. 

One  reason  for  emphasizing  a  case  of  this  kind  is  to  show  how 
impossible  it  is  to  establish  set  rules  in  factory  lighting.  To 
do  so  may  result  in  disadvantages  to  certain  workmen  where 
the  work  is  of  a  special  nature,  and  no  amount  of  argument  will 
change  the  actual  state  of  affairs.  We  must  adapt  the  illumina- 


Twin  Flexible  Deck 
*S        Cable         \ 


Wooden  Bushing 


V 


Attachment 

Wood  Guard 
for  Socket 
^ 

w™ 

Hook  for 

Su  pporting 

Lamp 

Reflector 

FIG.  100. — Extension  line  for  individual  hand  lamp  for  use  in  shops  and 
designed  specifically  for  long  wear  under  rough  conditions. 


tion  to  the  requirements  of  vision  and  not  compel  vision  to 
accommodate  itself  to  unsuitable  illumination.  Let  the  illuminat- 
ing engineer  or  the  foreman  take  the  place  of  the  workman, 
looking  at  what  he  must  see  and  observing  whether  the  conditions 
are  right.  The  workman  may  know  that  conditions  are  not 
right,  and  not  know  why  nor  what  the  proper  remedy  may  be. 
He  may  ask  for  a  certain  kind  of  lamp  when  the  difficulty  would 
be  best  obviated  by  something  entirely  different. 


MACHINE  TOOL  LIGHTING  155 

106.  Candle-power  of  Individual  Lamps. — By  directing  the 
light  to  the  point  where  most  needed  with  a  reflector,  it  may  be 
possible  to  reduce  the  size  of  an  individual  lamp,  that  is,  to  use  a 
smaller  lamp  than  otherwise.     This  should  be  left  to  the  judg- 
ment of  the  foreman  in  charge,  and  while  the  operating  man  is 
interested  in  lowering  the  energy  and  maintenance  charges  in 
every  possible  way,  the  use  of  a  smaller  lamp  should  not  be  based 
on  the  saving  in  energy,  but  on  whether  the  work  can  be  per- 
formed  satisfactorily   with    a    smaller   lamp.     Hence,  whether 
the  lamps  are  to  be  made  smaller  or  larger,  a  step  of  this  kind 
should  only  be  taken  if  there  are  distinct  advantages  to  the  work- 
men by  so  doing. 

The  intensity  of  the  illumination  furnished  by  individual 
lamps  close  to  the  work  is  ordinarily  as  great  as  that  considered 
adequate  from  over-head  lamps,  but  it  is  usually  on  a  small 
space  and  the  eye  under  these  conditions  requires  more  light 
than  otherwise.  If,  therefore,  tests  are  undertaken  to  find 
whether  the  individual  lighting  is  sufficient,  something  should 
be  allowed  for  the  additional  illumination  needed  from  the  indi- 
vidual lamp  over  and  above  that  which  might  be  enough  from 
lamps  mounted  well  over-head. 

107.  Concluding    Items. — The    underlying    thought    in    all 
illumination  work  in  the  factory  should  be  effectiveness.     This 
is  of  course  true  in  the  mounting  of  individual  lamps  and  in 
directing  the  light  from  these  lamps  where  it  is  most  needed. 
Attention  should,  however,  be  drawn  again  to  the  relatively 
great  advantages  of  the  over-head  lighting  method  wherever  this 
scheme  can  take  the  place  of  individual  lamps,  but  where  the 
latter  are  necessary,  they  should  be  supplied  without  hesitation. 

Factory  foremen  can  co-operate  with  the  workmen  in  show- 
ing them  how  to  use  the  individual  lamps  and  to  appreciate 
the  simple  principles  of  illumination  affecting  their  workman- 
ship. The  imparting  of  such  information  to  the  workmen  is  all 
the  more  important  when  one  considers  that  even  after  an  indi- 
vidual lamp  has  been  installed  with  due  regard  to  the  setting  of 
the  lamp  and  to  the  reflector  for  sending  the  light  in  the  right 
direction,  these  features  may  be  so  little  appreciated  by  the 
employe  that  they  may  not  be  used  to  good  advantage. 

To  the  other  factors  bearing  on  shop  economy,  satisfactory 
lighting  will  doubtless  be  added  in  the  near  future  even  in  those 
cases  where  but  little  attention  has  been  given  it  thus  far. 


156  FACTORY  LIGHTING 

Efforts  to  improve  the  illumination  and  to  reduce  the  glare  now 
so  often  prevalent,  should  ultimately  result  in  improved  eye- 
sight among  factory  workmen.  This  humane  consideration, 
when  taken  in  conjunction  with  the  other  economical  advantages 
afforded  by  such  improvements,  commends  artificial  lighting 
as  being  due  more  interest  and  attention  than  it  has  received 
during  past  years. 


INDEX 


Alba  reflectors,  92 

Am.  Inst.  of  Elec.  Eng.,  51 

American  Machinist,  95 

Arc  lamps,  bracket  for,  37 
flame  carbon,  1,  4,  5,  8 
in  power  house,  122 
maintenance  items  for,  52 
mesh  screen  for  globe,  39 
metallic  flame  or  magnetite,  1, 

4,5,8 
record  blank  for   maintenance 

of,  60 
wire  supports  for,  111 

Asso.  of  Iron  and  Steel  Elec.  Eng., 
143 


Basement  lighting  in  power  house, 

118 

Blooming  mill  lighting,  136 
Boiler  room  lighting  in  power  house, 

118 

Bolt,  toggle,  30 

Boring  mill,  support  for  lamp,  147 
Bracket  for  arc  lamp,  37 

for  machine  tool  lighting,   146 
Buildings  involved  in  steel  mills,  126 


Candle-power,  chart  of,  4 

of  lamps,  3,  155 

relation  to  mounting  height,  12 
Carbon  filament  lamps,  1,  3,  4,  5,  8 
Carpenter  shop  lighting,  138 
Ceiling,  conditions  in  factory,  102 

construction,  31 

height  in  factory,  101 

substitute  for,  95 

Chains  for  supporting  reflectors,  38 
Charts  for  maintenance  records,  59 


Circuits,  lighting,  106 

power  and  lighting,  separate,  40 
series  and  multiple,  39 
supply,  7,  40 

Classification  of  lighting,  general,  2 

Cleaning  reflectors  and  globes,  56 

Coal  bin  and  conveyor  lighting,  in 
power  house,  118 

Column  numbering,  55 

Control  circuits,  36 

Cooling  table  lighting,  134 

Cooper  Hewitt  lamp,  8 

Cost  factors,  drafting  room  lighting, 

93 

factory  lighting,  98, 113 
iron  and  steel  mill  lighting,  142 
machine  tool  lighting,  149 
office  lighting,  77 
of  wiring  per  outlet,  31 
power  house  lighting,  116 
relations,    artificial    light    and 

machine  tools,  149 
maintenance,  49 
wages  to  light,  99 

Crane  clearance,  4,  21 

D 

Data  of  iron  and  steel  mill  lighting^ 
•  systems,  140 

tungsten  lighting  systems,  26 
Daylight  conditions,  7 
Design,  illumination,  6 

problem,  20 
Dirt  on  reflectors,  losses  produced 

by,  46,  48,  49,  50,  51 
Drafting  room   lighting,    combined 
direct   and   indirect   light- 
ing for,  92 
complaints  of,  87 
cost  factors,  93 
difficult  conditions,  85 


157 


158 


INDEX 


Drafting  room  lighting,  eliminating 

shadows,  86 

fixture  combinations,  94 
four  lamp  fixtures  used  for,  91 
general  requirements  of,  85 
illumination  features,  93 
mercury  vapor  lamps  in,  97 
practical  investigation  of,  86 
substitute  ceiling  for,  95 


Economy  in  drafting  room  lighting/93 
factory  lighting,  98,  113 
iron  and  steel  mill  lighting,  142 
machine  tool  lighting,  149 
office  lighting,  77 
power  house  lighting,  116 
switch  control,  14 
wiring,  41 

Effective  illumination,  4 

Efficiency  of  lighting  system,  16,  22 
values,  17 

Electrical    considerations    in    steel 
mills,  125 

Electric  circuits,  table  of,  8 
Journal,  150 

Engine  room  lighting  in  power  house, 
117 

Erecting  shop  lighting,  133 

Estimates,  30 

Extension  lines,  152,  154 


Factory  lighting,  ceiling  conditions 

102 

height,  101 

cost  factors,  98,  99,  113 
field  of  various  lamps  in,  104 
general  requirements,  102 
nature  of  work,  101 
new  ideas  of,  98 
new  lamps  available  for,  98 
over-head  method,  103 
popular  ideas  of,  100 
practical  case,  high  mounting, 

110 

moderate  ceiling  height,  107 
relation    of    wages    to    lighting 
costs,  98,  99,  113 


Factory  lighting,  space  conditions 
between  floor  and  ceiling, 
101 

surroundings,  102 
various  items  included   under, 

101 

Flame  carbon  arc  lamps,  1,  4,  5,  8 
Flanging  shop  lighting,  134 
Flux,  light,  16 

Following  up  wiring  work,  34 
Foot-candle,  17 
Foundry  lighting,  130 


Gas  lamps,  1 

Gem  lamps,  8 

General  lighting,  3 

Glass    and    metal    reflectors    com- 
pared, 104 

reflectors,  points  to  be  consid- 
ered, 105 

H 

Hand  rack  for  reflectors,  57 
Holders,  reflector,  36 
Holophane  Company,  9 
reflectors,  9,  14 


Illumination  2,  4 

design,  6 

quality  of,  5 

rule,  18,  19 

special  note,  27 

uniformity  of,  9 

Indirect  and  semi-indirect  lighting, 
83 

substitute  ceiling  for,  95 
Inspecting  lighting  systems,  52 
Inspection   of    the    location   to   be 
lighted,  6 

report,  54,  55 

route,  53 
Installation  work,  28 

a  few  lamps  at  a  time,  43 

in  relation  to  maintenance,  41 
Intensity  values,  recommended,  23 

standards  of,  129 


INDEX 


159 


Iron  and  steel  mill  lighting,  adapta- 
tion of  lamps  to,  130 

blooming  mills,  136 

buildings  involved,  126 

cooling  tables,  134 

cost  factors,  142 

electrical  considerations,  125 

erecting  shops,  133 

flanging  shops,  134 

foundry,  130 

general  items,  125 

general  requirements,  127 

hot  metal  as  a  factor,  139 

importance     of     over-heading 
lighting,  128 

laying  out  floors,  134 

loading  sheds,  137 

machine  shops,  132 

maintenance  of,  139 

open-hearth  furnaces,  132 

pattern   and   carpenter   shops, 
138 

yards,  139 

Items  involved  in  a  lighting  system, 
58 


Lamps,  candle-power  of  individual, 

155 

carbon  filament,  1,  3,  5,  8 
field  of  various  types,  104 
flame  carbon  arc,  1,  4,  5,  8 
gas,  1 
gem,  8 

mercury  vapor,  1,  4,  5,  8 
metallic  flame  or  magnetite  arc, 

1,  4,  5,  8 
metallized  filament  or  gem,  1, 

4,8 

Moore  tube,  1',  4 
Nernst,  1,  4,  5,  8 
physical  size  of,  5,  152 
renewal  of,  47 
size  of,  discussed,  10,  21 
spacing  of,  12,  21,  74,  77 
supporting  the,  35 
switch  control  of,  14,.  25 
tantalum,  1,  4 
tungsten,  1,  4,  5,  8,  42 


Lamps,  types  of,  10,  21,  104 

Quartz,  1,  4,  5 

Laying  out  floor  lighting,  134 
Light,  2 

flux,  16 

quality  of,  5 

side  components  of,  13,  105 
Lighting  circuits,  106 
Lighting  systems,  inspection  of,  52 

items  included  under,  58 
Loading  shed  lighting,  134 
Locating  the  outlets  on  the  ceiling, 

44 
Losses  due  to  dirt  on  reflectors,  48, 

49,  50,  51 

Low  ceilings,  difficulties  of,  3 
Lumen,  16,  22 

M 

Macbeth-Evans  Glass  Co.,  92 
Machine  shop  lighting,  132 
Machine  tool  lighting,  bracket  for, 

146 

candle-power  of  lamps  for,  155 
charges  per  hour  against  ma- 
chine tool,  152 
concentrating  the  light,  147 
cost  relations,  149 
extension  lines,  152,  154 
importance  of  sufficiency,  144 
mounting    the    lamps    on    the 

tools,  146 

over-head  lamps  for,  144 
physical  size  of  lamps  for,  152 
shadow  contrasts,  153 
support  for  lamp  on  boring  mill, 

147 
Maintenance,  46 

cost  relations,  49 
importance  of  system,  47 
items-  involved,  51,  52 
record  blanks  for,  59,  60,  61 
records  for,  57 
relation  to  in.stal.at ion.  41 
report  on  inspection,  54,  55 
results  of  care  in,  62 
simplicity  essential,  61 
standards  in  equipment,  62 
storage  of  materials,  62 


160 


INDEX 


Maintenance,  table  of  information, 

tungsten  lamps,  59 
truck  for,  56 
washing  division^  56 

trough,  58 

Mercury  vapor  lamps,  1,  4,  5,  8 
in  drafting  room,  97 
in  power  house,  122 
record  blanks  for  maintenance 

of,  60 
Mesh  screen,  for  globes,  39 

for  reflectors,  36 
Metal  and  glass  reflectors  compared, 

104 
Metallic    flame    or    magnetite    arc 

lamps,  1,  4,  5,  8 
Metallized  filament  or  gem  lamps, 

1,  4,  5,  8 

Moore  tube  lamp,  1,  4 
Mounting  height  of  lamps,  13,  23 

N 

National  Elec.  Light  Asso.,  52 
Nernst  lamp,  1,  4,  5,  8 
New  ideas  of  lighting,  1 
Numbering  columns,  55 

O 
Office  lighting,  cost  factors,  77 

design  factors,  74 

general  requirements,  65 

high  ceilings,  76 

indirect  and  semi-indirect  light- 
ing, 83 

investigation  of  typical  room,  66 

narrow  room,  78 

odd  dimensions,  76 

practical  example,  75 

rectangular  room,  81 

simple  rules,  72 

small  room,  79 

spacing  distances  of  lamps  in, 

74,  77 

Open-hearth  furnace  lighting,  132 
Over-all  dimensions  of  lamps,  chart,  5 
Over-head    lighting     for     machine 
tools,  144 

in  factory  buildings,  103 

in  iron  and  steel  mills,  128 


Pattern  shop  lighting,  138 

Physical  dimensions  of  lamps,  3,  4 

Point  additions,  17,  23 

Popcke,  A.  G.,  150 

Power  house  lighting,  arc  lamps  in, 

122 

basement,  118 
boiler  room,  118 
coal  bins  and  conveyors,  118 
economy  of  good  lighting,  116 
engine  room,  118 
general  hints,  124 
general  requirements,  115 
intensity  required,  123 
maintenance  of,  124 
mercury  vapor  lamps  in,  122 
modern  viewpoint,  116 
practical    case,    medium    sized 

lamps,  119 

relation  to  operation,  115 
simple  principles  important,  122 
transformer  compartments,  118 
tungsten  lamps  in,  120 
water  gages,  124 

Practical  features  of  lighting,  2 

Pull  switch,  37 

Q 

Quality  of  light  and  illumination,  5 
Quartz  lamp,  1,  4,  5 


Records  of  maintenance,  46,  57,  59 

arc  lamps,  60 

mercury  vapor  lamps,  61 

tungsten  lamps,  60 
Redirection  of  liglit,  9 
Reflectors  and  globes,  9 

alba,  92 

chains  for  supporting,  38 

cleaning,  56 

glass  and  metal  compared,  104 

hand  rack  for  carrying,  57 

holders  for,  36 

holophane,  9,  14 

losses  due  to  dirt,  46,  48,  49,  50 
51 


INDEX 


161 


Reflectors      and      globes,     meshed 

screens  for,  36,  39 
points  to  be  considered,  105 
truck  for  handling,  56 
washing  division,  56 

trough  for,  58 
Renewel  of  lamps,  47 
Report  on  inspection,  maintenance, 

54,  55 

Requirements  of,  drartingroom  light- 
ing, 85 

factory  lighting,  102 
iron  and  steel  mill  lighting,  127 
office  lighting,  65 
power  house  lighting,  115 
Results  of  good  lighting,  1 
Rule  for  calculations,  18,  19 
Rules,  for  office  lighting,  72 
Underwriters',  34 

S 

Scale  of  drawing,  16 
Semi-indirect  lighting,  83 

substitute  ceiling  for,  95 
Shadow  contrasts,  153 

effect  and  spacing  of  lamps,  11 

elimination,  86 
Shop  lighting,  132 
Side  components  of  the  light,  13,  105 
Size  of  lamps,  10,  21 
Space  between  floor  and  ceiling,  7 
Spacing  and  shadow  effect,  11 

of  lamps,  12,  21,  74,  77 
Specifications,  16 
Specific  lighting,  3 
Standards  in  lighting  equipment,  62 
Storage  in  maintenance  division,  62 
Stringer  boards,  45 
Substitute  ceiling  for  semi-indirect 
lighting,  95 


Supply  circuits,  7,  40 
Supporting  the  lamps,  35 
Switch,  control,  14,  25 
economy  of,  14 
indication  of,  16 
pull,  37 
wall,  36 


Tantalum  lamp,  1,  4 

Toggle  bolt,  30 

Transformer   compartment  lighting 
in  power  house,  118 

Truck  for  maintenance,  56 

Tungsten  lamp,  1,  4,  5,  8,  42 
in  power  house,  120 
inspection  report  for,  55 
maintenance  items  of,  51,  52 
record   blank   for   maintenance 

of,  60 
table  of  information  for,  59 

Type  forms,  lighting  of,  96 
of  lamp,  10,  21,  104 

U 

Underwriters'  rules,  34 
Uniformity  of  illumination,  9 

W 

Wages,  relation  of  lighting  costs  to, 

99 

Wall  switch,  36 
Washing  division  for  reflectors,  56 

trough,  58 

Water  gages  in  power  house,  124 
Wiring  plan,  29,  41,  44 
Working  drawing,  15 


Yard  lighting,  139 


11 


RETURN  TO  the  circulation  desk  of  any 
University  of  California  Library 
or  to  the 

NORTHERN  REGIONAL  LIBRARY  FACILITY 
Bldg.  400,  Richmond  Field  Station 
University  of  California 
Richmond,  CA  94804-4698 

ALL  BOOKS  MAY  BE  RECALLED  AFTER  7  DAYS 
2-month  loans  may  be  renewed  by  calling 

(415)  642-6753 
1-year  loans  may  be  recharged  by  bringing  books 

to  NRLF 
Renewals  and  recharges  may  be  made  4  days 

prior  to  due  date 

DUE  AS  STAMPED  BELOW 


cm 

SEP 


JUL  2  6  1995 


flCT  0  9 1995 


JUL  2 11997 


JUN  1  2  2005 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


